Beat The ... Najdorf

IN this series I am looking at the statistically best way to play against popular opening lines.

The numbers are drawn from the 2021 edition of ChessBase's Mega database, ignoring, where possible, those results that include very few games and so are statistically insignificant.

The Sicilian Najdorf: 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 is a tough nut to crack.

Indeed the move 5...a6 scores 49% in Mega21. In other words, statistically speaking, Black has already all but equalised,

There are almost 210,000 games with the position after 5...a6.

Of White's replies that appear at least 10,000 times, the best-scoring is 6.f4, which chalks up 54%.

Position after 6.f4

Black has six main replies.

A) 6...e5 (3,948 games)

After 7.Nf3 the line splits.

A1 7...Nbd7 8.a4 Be7 9.Bd3 0-0 10.0-0, after which the line splits again.

A1.1 10...exf4 11.Bxf4!? Qb6+ 12.Kh1 Qxb2, when White scores 61% with both 13.Qe1 and 13.Nd5.

A1.2 10...Nc5 11.Kh1, with a further split: A1.2a 11...exf4 12.Bxf4 Bg4 13.Be3 Rc8 14.Qe2 scores 58% for White; A1.2b 11...d5 12.Nxe5, when 12...dxe4 13.Be2 scores 83% for White and 12...Ncxe4 13.Be3 scores 62% for White.

A2 7...Qc7 8.a4 (this scores 59%, as does 8.Bd3 - I have gone for the pawn move because it is slightly less well-known) Be7 9.Bd3 0-0 10.0-0, which scores 58% for White.

B) 6...e6 (2,456 games)

White scores 59% with 7.a4, edging out the 58% of the more-popular 7.Qf3, 7.Be2 and 7.Bd3.

B1 7...Be7 8.Be2, after which the line splits again.

B1.1 8...Qc7 9.0-0 brings a further split.

B1.1a 9...Nc6 10.Be3 0-0 11.Kh1 scores 56% for White.

B1.1b 9...0-0 10.Kh1 Nc6 11.Be3 reaches the same position as B1.1a.

B1.2 8...0-0 9.0-0 Nc6 (9...Qc7 is a transposition to B1.1b) 10.Be3 Qc7 is a transposition to B1.1a.

B2 8...0-0 9.0-0 Qc7 is a transposition to B1.1b while 9...Nc6 is a transposition to B1.2.

B3 8...Nc6 9.Be3 0-0 10.0-0 Qc7 is a transposition to B1.1a.

C) 6...Qc7 (2,350 games)

Transpositions to previous lines are possible, but White's score rises to 60% with 7.Qf3, to which Black has two main replies.

C1 7...g6 8.Be3 Bg7 9.h3, when the line splits again.

C1.1 9...0-0 reaches a position that occurs 14 times in Mega21. White scores 75% with 10.0-0-0.

C1.2 9...Nbd7 reaches a position that occurs 11 times in Mega21. White scores 80% with 10.0-0-0.

C2 7...Nc6 reaches a position that occurs 30 times in Mega21. In 20 of those games, White played 8.Be3, scoring 78%.

D) 6...Nbd7 (810 games)

After 7.Be2, the line splits.

D1 7...g6 8.Bf3!? Bg7 reaches a position that occurs 21 times in Mega21. White scores highly - at least 75% - with 9.g4, 9.Be3, 9.Nb3 and 9.Nde2, but none appears in the database more than four times.

D2 7...e5 8.fxe5 results in another split.

D2.1 8...dxe5 9.Nf5 scores 71% for White.

D2.2 8...Nxe5 reaches a position that occurs 10 times in Mega21. White scores 88% with 9.Bg5, but there are only four games.

D3 7...e6 8.Bf3 results in another split.

D3.1 8...Qc7 9.0-0, at which point the line splits again.

D3.1a 9...Be7 10.a4 0-0 11.g4 scores 82% for White.

D3.1b 9...Rb8 10.Kh1 b5 reaches a position that occurs 10 times in Mega21. White scores highly - at least 75% - with 11.e5, 11.Re1, 11.a3 and 11.Be3, but none appears in the database more than four times.

D3.2 8...Be7 9.0-0, at which point the line splits again.

D3.2a 9...0-0 10.Kh1 Qc7 11.a4 scores 85% for White.

D3.2b 9...Qc7 is a transposition to D3.1a.

E) 6...g6 (339 games)

After 7.Be2 Bg7 8.0-0 0-0 9.Kh1 the line splits.

E1 9...Nbd7 10.Be3 scores 56% for White.

E2 9...Nc6 10.Nb3 scores 63% for White.

E3 9...Qc7 10.a4 scores 86% for White.

F) 6...Nc6 (270 games)

Most popular is 7.Be2, which scores a very healthy 60%, but 7.Nf3!? scores an even better 68%, after which the line splits.

F1 7...e6 8.Bd3 leads to another split.

F1.1 8...Be7 9.0-0 0-0 10.Kh1 scores 71% for White.

F1.2 8...Qc7 9.0-0 Be7 10.Qe1 0-0 11.e5 scores an amazing 96% for White, albeit from only 14 games.

F1.3 8...b5 9.0-0 Bb7 10.Qe1 scores 71% for White, albeit from only seven games.

F2 7...Bg4 8.h3 Bxf3 9.Qxf3 scores a perfect 100% for White, albeit from only 12 games.

Bobby Fischer v The Sicilian (part two)

Sicilian Najdorf

Fischer almost always met the Sicilian with open lines, ie lines based on 2.Nf3, 3.d4 and (after 3...cxd4) 4.Nxd4.

One of the most-popular variations in his day and, if anything, even more popular today, was the Najdorf: 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6.

Fischer usually met this with the aggressive 6.Bc4.

Position after 6.Bc4

Black almost always replies 6...e6 - more than 90% of the time in Mega20 - but it is as well to know why other plausible ideas are not to be feared.

Black alternatives to 6...e6

A) 6...b5 is usually a harmless transposition after 7.Bb3 e6, but Black should avoid 7...b4? as White has 8.Nd5, when 8...Nxe4, the most-popular move in Mega20, runs into 9.Qf3 Nc5 (best, but insufficient) 10.Nxb4 Nxb3 11.axb3 Ra7 12.Ndc6.

B) 6...Nxe4? looks silly after 7.Qh5 (other moves also give a winning advantage), eg 7...e6 8.Nxe4 d5 9.Ng5 g6 10.Qf3, after which Black is a piece-for-a-pawn down.

Early in his career, Fischer usually met 6...e6 with 7.0-0, but he came to prefer 7.Bb3, and that is what I am recommending.

The move ensures neither ...b5 nor ...d5 can come with tempo against the light-square bishop, and similarly rules out ...Qc7 or ...R(either)c8 coming with tempo against the same bishop. It also prevents the knight-fork trick ,,,Nxe4 followed by ...d5.

Black plays 7...b5

This is recommended by Tony Kosten in Easy Guide To The Najdorf (Everyman 1999). Fischer usually played the mainline 8.0-0.

A) 8...Be7 (easily the most-popular move in Mega20) 9.Qf3 Qc7 (Kosten gives this an exclamation mark - Black should avoid 9...0-0? 10.e5 dxe5 11.Nxe6 and 12.Qxa8).

This position first appears in Mega20 in the following game.

Fischer - Friðrik Ólafsson

Buenos Aires 1960

10.Qg3

This is still overwhelmingly the choice today.

10...b4

The main line runs 10...0-0 11.Bh6 Ne8 12.Rad1 Bd7, when there is a divergence of opinion. Stockfish12 reckons White is better after 13.f4!?, which is marginally less popular than 13.Nf3; Komodo11.01 reckons Black has equal chances.

Kosten recommends 10...Nc6 11.Nxc6 Qxc6 12.Re1 Bb7. He gives this gambit move an exclamation mark, but the engines reckon 13.Qxg7 Rg8 14.Qh6 0-0-0 15.Qh3 Kb8 16.f3 Rg6 17.Be3 Rdg8 18.Re2 is better for White, despite Kosten's suggestion of 18...h5 or 18...Bd8 in place of 18...Nd7, which was played by Polugaevsky in a blindfold loss to Ivanchuk. However the position is far from clear.

11.Nce2 g6

The commonest move in Mega20 is 11...Nxe4?, but after 12.Qxg7 Bf6 13.Qh6 White is well on top (winning, according to Stockfish12).

After the text Fischer played 12.c3?! and only drew. The engines reckon White is comfortably better after 12.Bh6.

B) 8...Bb7 (this logical move is second in popularity in Mega20) 9.Re1 (Fischer played 9.Bg5 and 9.f4 earlier in his career, but in 1970 switched to what is the main line and is the engines' choice).

Fischer - Jorge Rubinetti

Interzonal (Palma de Mallorca) 1970

9...Nbd7

The normal move, and a typical placement for the queen's knight in the Najdorf. From d7 it supports the king's knight, eyes the e5 square and may go to c5 to swop off White's aggressively placed light-square bishop (although Black has to be careful to get the timing right).

10.Bg5

The engines prefer the little-played 10.a4!?, one line running 10...b4 11.Nd5! (a typical idea when White's king's rook is lined up against Black's uncastled king) exd5 12.exd5+ Be7 13.Nf5 Ne5 14.Nxg7+ Kd7 15.Nf5 with a big attack for White in Tomasz Warakomski (2375) - Jacek Szwed (2162), Polish U19 Team Championship 2005 (1-0, 30 moves).

Another interesting try is 10.Bxe6!? (another typical idea for White when Bc4 is played against the Najdorf) fxe6 11.Nxe6 Qc8 12.Nxf8!? (the engines prefer this to the more-common 12.Nd5) Rxf8 13.Qxd6 with an unclear position in which White has three pawns and an attack for a knight.

10...h6 11.Bh4 Nc5!?

Attacking the white light-square bishop is always tempting for Black, but the engines prefer 11...g5 12.Bg3 Ne5 with a tense position that may slightly favour White, according to the engines.

12.Bd5!

Perhaps Rubinetti missed that this was possible.

12...exd5?!

Russian grandmaster Valerij Popov played the same way in a 2006 loss, but grabbing the knight is almost certainly too greedy. However the engines reckon White is much better even after their preferred line: 12...Be7 13.Bxb7 (13.Nc6 is also strong) Nxb7 14.Nc6.

13.exd5+ Kd7

Or 13...Be7 14.Bxf6 gxf6 15.Nf5 etc.

14.b4 Na4 15.Nxa4 bxa4 16.c4 Kc8

Artur Kogan (2564) - Valerij Popov (2591), EU Team Cup (Fügen, Austria) 2006 saw 16...Kc7 17.Qxa4 g5 18.Bg3 Nh5 19.c5! Bxd5 (or 19...Nxg3 20.c6 Bc8 21.Qa5+ Kb8 22.Qxd8) 20.Rac1 Nxg3 21.cxd6+ Kb7 22.Rc7+ 1-0.

17.Qxa4 Qd7 18.Qb3!?

The engines strongly prefer 18.Qc2 for a reason I will explain later.

18...g5 19.Bg3 Nh5

Here the engines give 19...h5 20.Qf3 Rh6 21.Nf5 Rg6 22.h4 gxh4 23.Nxh4 Rxg3 24.fxg3, agreeing White is much better but possibly not winning (at least according to Komodo11.01). If the white queen were on c2 instead of b3 this line would be hopeless for Black because of 20.c5, eg 20...Bxd5 21.c6 Qg4 22.Qb2, when the engines reckon Black is busted.

20.c5! dxc5 21.bxc5 Qxd5

Or 21...Bxd5 22.Qb6 Qb7 23.Qa5 Nxg3 24.c6!? (the straightforward 24.hxg3 is also very good) Bxc6 (24...Qc7 25.Re8+) 25.Nxc6 Qxc6 26.hxg3 (not 26.Rac1?? Ne2+) Bc5 27.Rac1 etc.

22.Re8+ Kd7 23.Qa4+ Bc6 24.Nxc6 1-0

Black is helpless, eg 24...Kxe8 25.Re1+ Kd7 26.Na7+ Kd8 27.Re8#.

Black plays 7...Be7

The main reply is 8.0-0 but Fischer preferred 8.Be3 and especially 8.f4, which is only fourth-most popular in Mega20 but still packs a punch and is liked by the engines.

A1) 8...Qc7 (Fischer did not face this although it is the most-common move in Mega20) 9.f5 (this seems to give White good play however Black replies) e5 10.Nde2!? (the knight is destined for g3 and possibly h5) Nbd7 11.Bg5 0-0 12.Ng3 b5 13.Nh5 Bb7 14.Bxf6 Nxf6 (14...Bxf6!? may be an improvement, although White has promising kingside play after 15.0-0 or 15.Qg4!?) 15.Nxf6+ Bxf6, as seen in Ivan Radulov - Fernand Goethals, World Student Team Championship (Sinaia, Romania) 1965 (1-0, 32 moves). The engines reckon White would be much better after 16.Qd3.

A2) 9...exf5?! (this is much less popular than 9...e5) 10.Nxf5 Bxf5 (the only reasonable try, according to the engines, as 10...0-0?! 11.Nxe7+ Qxe7 12.0-0! is very good for White as 12...Nxe4?? loses the knight to 13.Qe1) 11.exf5 0-0. White usually castles here, but the engines much prefer 12.Be3!? with the idea of castling long, when White has promising kingside play and pressure against d6.

B) 8...0-0 9.Qf3 Qc7 10.f5!? (Fischer played 10.0-0 against Tal but castling here may be a little slow) Nc6 (this seems to have been first played by Polugaevsky in 1958 - more popular today is 10...e5 but 11.Nde2 b5 12.g4 b4 13.g5 bxc3 14.Nxc3! has chalked up three wins in three outings in Mega20) 11.Be3 Nxd4 12.Bxd4 b5. This position has been reached 55 times in Mega20. The engines like the somewhat-obscure 13.fxe6!? Bxe6 (the more-common 13...fxe6?! gives White a strong attack after 14.0-0-0) 14.0-0 (14.0-0-0!?) Bxb3 15.cxb3!? b4 16.Nd5 Nxd5 17.exd5 Rae8. This position was reached in Eric Chery (2155) - Éloi Relange (2490), Paris 1998. Relange went on to win, but the engines reckon White would have been better after the natural 18.Rac1.

C1) 8...b5!? (White always has to anticipate this thrust in the Najdorf, but here Fischer had prepared a strong answer) 9.e5 dxe5 10.fxe5 Nd5?! 11.Nxd5 exd5 12.Qf3. White is already winning, according to Stockfish12, although Komodo11.01 gives White 'only' the upper hand.

C2) 10...Nfd7!? (this has become the main move, but Black is teetering on a precipice) 11.Bxe6!? (the engines also like 11.Qg4!? and 11.Qf3!?, but no line is completely clear) Nxe5 (not 11...fxe6? 12.Nxe6 Qa5 - 12...Qb6 13.Nd5! - 13.Nxg7+ with a mating attack, eg 13...Kf7 14.Qh5+ Kxg7 15.Bh6+ Kg8 16.e6 etc) 12.Bxc8 Qxc8 13.Nd5. White has scored very well from here, the most-popular continuation being 13...Bc5 (the engines reckon 13...Nbc6!? may be better) 14.b4 Qd7! 15.Nf3 Bd6 16.0-0 with a slight edge for White.

D1) 8...Nbd7 9.Bxe6!? (Fischer played 9.Qf3 is a simul, but the text racks up a huge score in Mega20 and is very tricky to face) fxe6 10.Nxe6 Qa5! (the very plausible 10...Qb6 is inferior for a reason I will explain later) 11.Nxg7+ Kf7 12.Nf5 Nc5! (the engines' suggested improvement over the known 12...Nxe4? 13.Qh5+ Kf8 14.Qh6+ Ke8 15.Qe6 winning and 12...h5 13.Nxe7 Kxe7 14.Qf3 with a strong attack) 13.Nh6+ (13.Nxe7?! Ncxe4!) Kg7 14.e5. White has three pawns and an attack for a bishop. He seems to be better but the position is unclear.

D2) The reason 10...Qb6 is inferior is that after 11.Nxg7+ Kf7 12.Nf5 Black does not have 12...Nc5? as White wins with 13.Nxe7 Kxe7 14.Qd4 when Qxf6+! followed by Nd5+ is a winning threat. In this line the position of the black queen on b6 means he no longer has the resource 13...Ncxe4, which is simply met by 14.Nxe4, eg 14...Nxe4 15.Qd5+ Kxe7 16.Qxe4+, when White emerges two pawns up.

E) 8...Nc6 (Fischer did not face this unNajdorf-like move but it is a popular choice) 9.Be3 0-0 10.Qf3 Qc7 11.0-0-0. White scores an excellent 64% from this Scheveningen-type position. Most popular now is 11...Nxd4, which has been played by Kasparov, although after 12.Bxd4 (Kasparov's opponent chose the probably inferior 12.Rxd4?!) White has a winning attack, according to Stockfish12 (Komodo11.01 is much less sure of White's advantage). The main line continues 12...b5 13.Bxf6 Bxf6 14.e5 Bb7 15.Bd5! with a huge advantage, eg 15...exd5 16.exf6 or 15...Bxd5 16.Nxd5 exd5 17.exf6 or 15...dxe5 16.Bxb7 Rab8 17.Be4.

Black plays 7...Nbd7

There is only one game in Mega20 in which Fischer faced this move, which is recommended in Mastering The Najdorf by Julen Arizmendi and Javier Moreno (Gambit 2004), and he replied with the mainline 8.f4.

Black nearly always continues 8...Nc5, which is the chief point of playing an early ....Nbd7. White needs to react energetically, and Fischer chose 9.f5!?, which is the most-popular move in Mega20.

A) 9...Nfxe4?! 10.fxe6! Qh4+ (or 10...Bxe6 11.Nxe6 fxe6 12.Nxe4 Nxe4 13.Qg4 Nc5 14.0-0 with a big attack and the bishop-pair on an open board for a pawn) 11.g3 Nxg3 12.Nf3 Qh5 13.exf7+ Kd8 14.Rg1. Black is not even a pawn up. Fischer - Jacek Bednarski, Olympiad (Havana) 1966, continued 14...Nf5 15.Nd5! Qxf7 16.Bg5+ Ke8 (if 16...Be7 then simply 17.Nxe7 is devastating) 17.Qe2+ Be6 18.Nf4 Kd7 19.0-0-0 Qe8 (19...Bxb3 20.Ne5+) 20.Bxe6+ Nxe6 21.Qe4 g6 22.Nxe6 1-0.

B) 9...Nxb3 (Fischer reached this position via a slight transposition) 10.axb3 Be7 11.Qf3 0-0 12.Be3 Bd7 (more popular in Mega20, albeit from a small sample size, is the time-consuming 12...Nd7?!, but the engines reckon White has a sizeable advantage after 13.0-0-0) 13.g4. The engines reckon 13...d5!?, which is not in Mega20, keeps White's edge reasonably small. Instead Fischer - Carlos Bielicki, Mar del Plata (Argentina) 1960, saw 13...e5 14.Nde2 d5 15.exd5 e4 16.Qg2 Bb4 17.0-0-0. after which White's attack crashed through first (1-0, 38 moves).

C) 9...Be7. This, the chief response today, was not faced by Fischer. The main line goes 10.Qf3 0-0 11.Be3 e5 12.Nde2 Nxb3 13.axb3 b5!?  The position is unclear. White has dangerous threats on the kingside, and indeed 14.g4!? is the most-popular continuation, although the engines reckon 14...b4!? is a good answer and makes queenside castling unpalatable. Note that Black gets strong play after 14.Nxb5?! d5. Instead Stockfish12 gives 14.Nd5 Bb7 15.Nxf6+ Bxf6 16.Rd1 Qa5+ 17.c3 Be7 18.h4!? with unclear but dangerous play. Komodo11.01 reckons best-play involves Black sacrificing the exchange: 14.0-0 Bb7 15.Ng3 Re8 16.Rad1 b4 17.Na4!? d5 18.Nb6 d4!? 19.Nxa8 Qxa8 20.Bg5 Nxe4 21.Bxe7 Nf6 22.Qe2 Rxe7, which is also unclear despite Black only having a pawn for the exchange.

D) 9...Bd7 (given an exclamation mark by Arizmendi & Moreno) 10.Qf3 b5 (another move given an ! by A&M) 11.a3 Nxb3 (necessary, according to A&M, as otherwise White preserves the light-square bishop with Ba2) 12.cxb3!? (12.Nxb3 is also reasonable) Be7 13.Be3 Qc8. A&M also give this move an exclamation mark, claiming Black has equalised. However the engines reckon White has a slight pull after 14.0-0 0-0, eg Stockfish12 gives 15.Rad1 b4!? 16.axb4 Rb8 17.g4 h6 18.g5 hxg5 19.Bxg5, claiming White has a slight edge, a verdict with which Komodo11.01 agrees.

Champion Of Champions (part nine)

HERE is the tournament bracket after the round of 16.

Round of 16               Quarter-Finals            Semi-Finals
1. Steinitz
v----------------------------Carlsen
16. Carlsen (+102.5)
                                    v................................
8.Tal (+8.5)
v----------------------------Tal
9.Petrosian

6. Botvinnik (+66)
v----------------------------Botvinnik
11. Fischer
                                    v.................................
13. Kasparov
v----------------------------Alekhine
4. Alekhine (+21.5)

3. Capablanca
v----------------------------Kramnik
14. Kramnik (+12)
                                     v................................
5. Euwe
v----------------------------Karpov
12. Karpov (+11.5)

7. Smyslov (+18)
v----------------------------Smyslov
10. Spassky
                                     v................................
15. Anand
v----------------------------Lasker
2. Lasker (+50.5)

Quarter-Finals
Match One: Carlsen v Tal
Game One
Magnus Carlsen - Mikhail Tal
Sicilian Najdorf/Scheveningen
1.e4 c5 2.Nf3 d6
Tal has 144 games with 2...d6 in ChessBase's 2020 Mega database, compared with 99 for 2...e6 and 66 for 2...Nc6.
3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6
Tal played the text 68 times in Mega20 compared with 50 for 5...Nc6 and 30 for 5...e6.
6.Be3
Carlsen has played eight other moves here but 6.Be3 has been his favourite.
6...e6 7.f3
Carlsen has played the text and 7.g4 twice each, winning both times with 7.f3 but scoring just a draw with 7.g4.

As far as we can get - Tal did not face 7.f3

Komodo11.01 gives Carlsen a minuscule edge but Stockfish11 prefers Black, and the evaluations average out to an advantage for Tal of +19.5.

Game Two
Mikhail Tal - Magnus Carlsen
Spanish Closed
1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.0-0 Be7 6.Re1 b5 7.Bb3 0-0 8.c3 d6 9.h3 Nb8 10.d4 Nbd7 11.Nbd2 Bb7 12.Bc2 Re8 13.Nf1 Bf8 14.Ng3 g6 15.a4 Nb6
We have a new record for getting deep into a 'game'. Carlsen has played the text and 15...c5 once each, drawing with the former and losing with the latter, so 15...Nb6 wins on tiebreak. It is not a move Tal faced.

A new record for depth in this tournament

The engines give Tal an averaged advantage of +60, making him a runaway winner of the first quarter-final.
Here is the updated bracket.

Round of 16               Quarter-Finals              Semi-Finals
1. Steinitz
v----------------------------Carlsen
16. Carlsen (+102.5)
                                       v................................Tal
8.Tal (+8.5)
v----------------------------Tal (+79.5)
9.Petrosian

6. Botvinnik (+66)
v----------------------------Botvinnik
11. Fischer
                                       v.................................
13. Kasparov
v----------------------------Alekhine
4. Alekhine (+21.5)

3. Capablanca
v----------------------------Kramnik
14. Kramnik (+12)
                                        v................................
5. Euwe
v----------------------------Karpov
12. Karpov (+11.5)

7. Smyslov (+18)
v----------------------------Smyslov
10. Spassky
                                        v................................
15. Anand
v----------------------------Lasker
2. Lasker (+50.5)

Champion Of Champions (part four)

HERE is the tournament bracket after three matches.

Round of 16               Quarter-Finals
1. Steinitz
v----------------------------Carlsen
16. Carlsen (+102.5)

8.Tal (+8.5)
v----------------------------Tal
9.Petrosian

6. Botvinnik (+66)
v----------------------------Botvinnik
11. Fischer

13. Kasparov
v--------------------------
4. Alekhine

3. Capablanca
v--------------------------
14. Kramnik

5. Euwe
v--------------------------
12. Karpov

7. Smyslov
v--------------------------
10. Spassky

15. Anand
v--------------------------
2. Lasker

Now for the match-up I have been eagerly anticipating.

Round of 16
Match Four: Kasparov v Alekhine
Game One
Garry Kasparov - Alexander Alekhine
Queen's Indian
1.d4
Favoured over 1.e4 in Kasparov's games in ChessBase's 2020 Mega database by 691 to 639.
1...Nf6 2.c4 e6 3.Nf3 b6 4.a3!?
Twenty-six games with this move compared with 25 for 4.Nc3 and 20 for 4.g3.

Alekhine never faced 4.a3!?

Well, that was an anti-climax. The engines Stockfish11 and Komodo11.01 are not impressed with White's play, giving Kasparov an averaged advantage of just +4.
I hope game two will be more interesting.

Game Two
Alexander Alekhine - Garry Kasparov
Sicilian Najdorf
1.e4 c5
I am intrigued to see how Alekhine will deal with Kasaprov's Najdorf.
2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3
Only just - there are four Alekhine games in Mega20 with the text and three with 5.f3!?
5...a6

As far as we can get - Alekhine never faced 5...a6

Another anti-climax. The engines's averaged evaluation gives Alekhine a score of +25.5, meaning he wins the match with a score of +21.5.
Here is the updated tournament bracket.

Round of 16               Quarter-Finals
1. Steinitz
v----------------------------Carlsen
16. Carlsen (+102.5)

8.Tal (+8.5)
v----------------------------Tal
9.Petrosian

6. Botvinnik (+66)
v----------------------------Botvinnik
11. Fischer

13. Kasparov
v----------------------------Alekhine
4. Alekhine (+21.5)

3. Capablanca
v--------------------------
14. Kramnik

5. Euwe
v--------------------------
12. Karpov

7. Smyslov
v--------------------------
10. Spassky

15. Anand
v--------------------------
2. Lasker

Note that the older generation has won three of the four matches in the top half of the bracket.

Champion Repertoire (part 13)

GARRY Kasparov was world champion from when he beat Anatoly Karpov in 1985 until he lost to Vladimir Kramnik in 2000.
A repertoire based on his games features theoretically sharp and deep lines, especially with the black pieces.
White
Kasparov's most-common opening move was 1.d4, which becomes more clearly dominant if one also includes games that began 1.c4 Nf6 2.d4. After 1...Nf6 2.c4 e6 he generally avoided the Nimzo-Indian and instead played 3.Nf3.
Against the Queen's Indian: 3...b6 he played in almost equal numbers a3, Nc3 and g3, but easily scored best (83%) with 4.a3, which was also (narrowly) his first choice. The main line continues 4...Bb7 5.Nc3 d5 6.cxd5 Nxd5, at which point Kasparov liked 7.e3, and if 7...Be7 (the normal reply) he played 8.Bb5+ c6 9.Bd3. Today's popular fourth-move alternative for Black, 4...Ba6, only features once in Kasparov's games in ChessBase's 2020 Mega database. He won after going down the mainline 5.Qc2 Bb7 6.Nc3 c5 7.e4 cxd4 8.Nxd4 Bc5 9.Nb3 Nc6 10.Bg5.
If Black switched to the Queen's Gambit Declined with 3...d5 Kasparov liked 4.Nc3, often also reaching the position from the move-order 1...d5 2.c4 e6 3.Nc3 Nf6 4.Nf3. After 4...Be7 5.Bg5 h6 (the most popular choice with Kasparov's opponents) he liked 6.Bxf6!? Bxf6 7.e3 0-0 8.Rc1. But after 5...0-0 6.e3 h6, rather than transposing to the previous line, he usually played 7.Bh4!? Clearly there is nothing wrong with this approach - it served Kasparov well enough! - but for the practical club player it may be better, at least at first, to study only Bxf6 or Bh4 systems. If Black went for a Semi-Slav set-up with 4...c6, a position Kasparov often reached from a Slav move-order: 1...d5 2.c4 c6 3.Nf3 Nf6 4.Nc3 e6, Kasparov mainly played 5.Bg5, meeting 5...dxc4 with 6.e4 b5 7.e5 h6 8.Bh4 g5 9.Nxg5 hxg5 10.Bxg5 Nbd7 11.exf6 Bb7 12.g3 (there are more than 1,200 games with this position in Mega20). Not all blacks fancy the complications and deep theory of 5...dxc4, which is why by far the most-popular move is 5...Nbd7, which Kasparov usually met with 6.e3, allowing the Cambridge Springs Defence: 6...Qa5, which he normally met with 7.Nd2 Bb4 8.Qc2. Against the Ragozin: 4...Bb4 Kasparov liked 5.cxd5 exd5 6.Bg5.
Against the Bogo-Indian: 3...Bb4+ Kasparov liked the slightly unusual 4.Nc3!?, after which the main line runs 4...b6 5.Bg5 Bb7 6.e3 h6 7.Bh4 g5 8.Bg3 Ne4. Kasparov reached this position four times, scoring a win and a draw with 9.Qc2 and two wins with 9.Nd2.
Against 3...c5 Kasparov varied his replies, narrowly favouring another slightly unusual move, 4.e3.
Against the King's Indian: 2...g6 3.Nc3 Bg7 4.e4 d6 he scored 88% with 5.Nf3, normally going down the mainline 5...0-0 6.Be2 e5, but then preferring the slightly unusual 7.Be3 (and if 7...Ng4 then 8.Bg5).
Against the Grünfeld: 3...d5 Kasparov liked 4.cxd5 Nxd5 5.e4 Nxc3 6.bxc3 Bg7 7.Nf3 c5, four times continuing 8.Be3 and three times 8.Rb1.
Against the Benoni: 2...c5 3.d5 e6 4.Nc3 exd5 5.cxd5 d6 6.e4 g6 Kasparov liked 7.f4 Bg7 8.Bb5+, meeting the main reply 8...Nfd7 with 9.a4 0-0 10.Nf3. Against the Benko Gambit: 3...b5 he liked 4.cxb5 a6 5.b6.
I have covered much of the Queen's Gambit Declined: 1...d5 2.c4 e6 3.Nc3 above, but that leaves the Alatortsev: 3...Be7, which Kasparov liked to meet with 4.cxd5 exd5 5.Bf4 (4.Nf3 Nf6 would be a simpler repertoire fit), and the Tarrasch: 3...c5, which Kasparov only faced four times, twice playing 4.e3!? and twice playing the main move 4.cxd5.
I also covered the Semi-Slav above, but against the pure Slav: 2...c6 3.Nf3 Nf6 4.Nc3 dxc4 Kasparov liked 5.a4 Bf5 6.e3 e6 7.Bxc4 bb4 8.0-0, usually meeting 8...0-0 with 9.Qe2 but preferring against 8...Nbd7 the somewhat unusual 9.Qb3 a5 10.Na2 Be7 11.Nh4!?, declining to grab the b7 pawn whether Black continued 11...Bg6 or 11...Be4.
Against the Queen's Gambit Accepted: 2...dxc4 he liked 3.e4 e5 4.Nf3 exd4 5.Bxc4.
Against 1...d6 Kasparov liked 2.e4 Nf6 3.f3!? g6 4.Be3 0-0 5.Qd2 with what can be thought of as an Accelerated 150 Attack!
Against the Dutch: 1...f5 Kasparov mostly played 2.Bg5!?
Against 1...e6 he usually transposed to a French: 2.e4 d5, scoring best (92%!) with the Tarrasch: 3.Nd2. A simpler repertoire choice is to allow a delayed Dutch with 2.c4 f5, after which 3.g3 Nf6 4.Bg2 is a position Kasparov reached in three games, winning them all.
Black v 1.e4
Play 1...c5 aiming to reach a Sicilian Najdorf: 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6.
Against 6.Be3 he mainly played 6...e6 and was happy to follow the mainline 7.f3 b5 8.Qd2 Nbd7 9.g4, at which point he played both the equally popular moves 9...Nb6 and 9...h6, scoring better with the former.
Against 6.Be2 he mainly played 6...e6 and was happy to follow the mainline 7.0-0 Be7 8.f4 0-0 9.Kh1 Qc7 10.a4 Nc6 11.Be3 Re8 12.Bf3 Rb8 13.g4 Nxd4 14.Bxd4 e5 15.fxe5 dxe5 16.Ba7 Ra8 17.g5 Rd8 18.Qe2 Ne8 19.Be3 Be6 20.Qf2. Kasparov reached this position twice, beating Topalov with 20...Qc4 and drawing with Anand with 20...Rdc8. This is an example of how deep the theory goes in some of Kasparov's favourite lines.
Against 6.Bc4 he played 6...e6 but after the main reply 7.Bb3 he tried four different moves. Most popular with Kasparov were 7...Nbd7 and 7...b5, but he scored 14 percentage points higher with the latter, which is the main move in the position. Play usually continues 8.0-0 Be7 9.Qf3 Qc7 10.Qg3 0-0 11.Bh6 Ne8 12.Rad1 Bd7, which Kasparov reached three times, scoring a win and two draws.
Against 6.Bg5 he mainly played 6...e6 but after the main reply 7.f4 his favourite move was 7...Qb6, being happy to enter the famous poisoned pawn variation 8.Qd2 Qxb2, meeting 9.Rb1 Qa3 10.f5 Nc6 11.fxe6 fxe6 12.Nxc6 bxc6 13.e5 dxe5 14.Bxf6 gxf6 15.Ne4 with the slightly unusual 16...Qxa2. If White did not offer the b2 pawn, instead playing 8.Nb3, Kasparov played the slightly unusual 8...Be7.
Against 6.f4 he mainly played 6...e6, meeting 7.Qf3 mainly with 7...Qb6 (this and 7...Qc7 are equally popular in Mega20 but Kasparov's choice scores 10 percentage points better). After the main reply 8.Nb3 he played 8...Qc7!?
Against 6.f3 he mainly played 6...e6, when all of his opponents continued 7.Be3, transposing into the 6.Be3 line already covered.
Against 6.h3 he played 6...e6, when the main move is 7.g4. Kasparov faced this three times, drawing with 7...Nfd7 but winning with 7...Be7 and 7...h6.
Against 6.a4 he played 6...Nc6 7.Be2 e6 (Black's sixth and seventh moves could safely be reversed for repertoire simplicity's sake), and against 6.g3 he played 6...e5.
Knowledge of a lot of theory is needed to follow Kasparov in the Najdorf, but note that with exception of 6.g3 all responses centre on playing ...e6 rather than ...e5.
Against the Hungarian Variation: 4.Qxd4 Kasparov narrowly preferred 4...a6 to 4...Nc6 or 4...Bd7.
Against the Moscow Variation: 3.Bb5+ he mainly played 3...Bd7 4.Bxd7+ Qxd7.
Against the 2.Nc3 he varied his responses but scored best (81%) with 2...d6, which is probably the best repertoire choice as if White switches to an Open Sicilian with 3.Nf3/Nge2 Nf6 4.d4 cxd4 5.Nxd4 Black gets a Najdorf with 5...a6.  Against the Closed Sicilian continuation 3.g3 Kasparov played 3...Nc6 4.Bg2 g6 5.d3 Bg7, at which point he played 6...Nf6 against both 6.f4 and 6.Be3, although against the latter he did also experiment with 6...Nd4. Against the Grand Prix Attack continuation 3.f4 he twice played 3...g6 4.Nf3 Bg7 and once played 3...Nc6 4.Nf3 g6.
Against the GPA without 2.Nc3, ie 1.e4 c5 2.f4 he played 2...d5 3.exd5 Nf6.
Against the Alapin: 2.c3 Kasparov played all three main replies, scoring 50% with ...d5 but 70% with ....Nf6 and 75% with ...e6. However his rating performance with ...e6 was more than 200 points lower than with my repertoire recommendation 2...Nf6.
Against 1.d4 and Others
Against 1.d4 aim for a King's Indian Defence: 1...Nf6 2.c4 g6 3.Nc3 Bg7 4.e4 d6.
Against 5.Nf3 0-0 6.Be2 he mainly played 6...e5 7.0-0 Nc6 8.d5 Ne7, mainly meeting 9.Ne1 with 9...Nd7. mainly meeting 9.b4 with 9...Nh5 and mainly meeting 9.Nd2 with 9...a5. If White played 7.d5 he mainly replied 7...a5 8.Bg5 h6 9.Bh4 Na6.
Against 5.f3 he mainly played 5...0-0 6.Be3 e5, meeting 7.Nge2 with 7...c6 8.Qd2 Nbd7 and mainly meeting 7.d5 with 7...c6, usually following up with a quick ...cxd5.
Against 5.Be2 0-0 6.Bg5 he mainly played 6...c5 7.d5 h6, meeting both 8.Be3 and 8.Bf4 with 8...e6.
Against 5.f4 0-0 6.Nf3 he mainly played 6...c5 7.d5 e6.
Against 5.h3 he played 5...0-0 6.Bg5 he liked the unusual 6...c6.
Against 3.Nf3 Bg7 4.g3 he mainly played 4...0-0 5.Bg2 d6 6.0-0 Nbd7 7.Nc3 e5 8.e4 c6.
Against 3.g3 Bg7 4.Bg2 he equally liked 4...d5 and 4...0-0, but the latter is much the simpler repertoire choice.
Against 2.Nf3 he equally played 2...d5 and 2...g6, but scored 17 percentage points higher with the latter, which again is the simpler repertoire choice. If White makes it a London System with 3.Bf4 Kasparov scored best (83%) with 3...d6 4.e3 Nh5 5.Bg5 h6 6.Bg4 g5. He only faced the New London: 2.Bf4 once, replying 2...c5.
He faced the Trompwosky: 2.Bg5 nine times, winning all three games that continued 2...d5 3.Bxf6 exf6. However 2...d6, which was also played three times by Kasparov, is arguably the better repertoire choice. Two of those games continued 3.Bxf6 exf6 4.e3 f5 5.g3 6.Bg2 Bg7 7.Ne2 Nd7.
Against the English: 1.c4 he mostly replied 1...g6, heading for a pseudo-King's Indian set-up, eg 2.Nc3 Bg7 3.g3 e5 4.Bg2 d6. But he did not slavishly stick to King's Indian-style moves, eg he three times faced 5.d3, drawing with 5...Nc6 but winning twice with 5...f5.
Against 1.Nf3 he mostly played 1...Nf6 with obvious transpositional possibilities, being happy to duplicate White's moves in the line 2.g3 g6 3.Bg2 Bg7 4.0-0 0-0, at which point Kasparov's opponents did not play the King's Indian Attack move 5.d3, which is popular at club level. Instead they mostly played either 5.d4, which Kasparov usually met with 5...d5 rather than the KID repertoire-friendly 5...d6, and 5.c4, which Kasparov met equally often with 5...c5 and the repertoire-friendly 5...d6.
Kasparov faced 1.b3 three times, twice playing 1...e5 and once playing 1...Nf6, but in each case following up with a quick ...g6 and ...Bg7.

Kasparov has played many famous games but I have chosen what may be his first competitive use of the Sicilian Najdorf.
Levon Eolian - Kasparov
Caucasas Youth Games (Tbilisi) 1976
1.e4 c5 2.Nf3 d6 3.d4 exd4 4.Nxd4 Nf6 5.Nc3 a6 6.Bg5 e6 7.f4 b5!?
This move is only sixth-most popular in Mega20 but is certainly not obscure as it the famous - notorious, some would say - Polugaevsky Variation. Nakamura, Ivanchuk and van Wely are among modern grandmasters who have played it.
8.a3!?
This is played from time to time by GMs but according to Richard Palliser in Starting Out: Sicilian Najdorf (Everyman Chess 2006) "White can and should aim to pursue the initiative with 8.e5 as slower plans give Black a good game."
8...Bb7 9.Qe2 Be7 10.0-0-0!?
Castling queenside after playing a3 with a black pawn on b5 looks like asking for trouble, but the move had been played by Spassky.
10...Nbd7 11.g4 Qb6
Spassky - V A Tatarintsev, Kislovodsk 1960, saw 11...Rc8 12.Bxf6 gxf6 13.Qe1!? Qb6 with an unclear position (1-0, 36 moves).
12.Bh4!?
My main analysis engines Stockfish11 and Komodo11.01 like this retreat, which clears the g5 square for the white g pawn and makes possible the further, but counterattacking, retreat Bf2.
12...Nc5 13.Bg2 Na4?!
The engines much prefer the obvious 13...b4 14.axb4 Qxb4, although the position remains very sharp.
14.Nxa4 bxa4 15.g5?!
The harassing retreat 15.Bf2 looks stronger.
15...Nd7 16.Be1!?
The bishop is coming to c3, from where it will eye Black's kingside as well as protect White's queenside.
16...0-0 17.h4 Rab8 18.Bc3 Rfc8 19.Rh3
Defending against a classic Sicilian exchange sacrifice on c3 (although normally the white piece there is a knight).
19...Ba8
Renewing the threat, but White overlooks it.
20.Qg4?!
The engines reckon White should have placed the queen so it can recapture on c3 and thus defend b2.
20...Rxc3! 21.bxc3
Not 21.Rxc3? Qxb2+ 22.Kd2 Bd8! with a crushing attack.
21...Nc5 22.f5 e5 23.Ne2?!
The consistent 23.f6 is probably better although the engines cannot agree on the merits of their critical lines, eg 23...exd4 34.fxe7 Bc6 35.Rxd4 Qb2+ 36.Kd1 Bd7 is winning for White, according to Stockfish11 but Komodo11.01 reckons Black has almost full compensation for his material deficit (he has a knight for a rook and pawn).
23...d5?
This seems a mistake. The engines reckon Black is better after 23...Qb2+ 24.Kd1 Bc6.
24.f6??
A move too late. White is much better, according to the engines, after 24.exd5.

What has White missed?

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24...Ne4 25.Bxe4
Forced as 25.fxe7?? allows two mates-in-one, but now Black has the zwischenzug ...
25...Bxa3+
After the further moves ...
26.Kd2 dxe4
... White is the exchange up and Black has multiple pawn weaknesses, but the key factor is the weakness of the white king.
27.Ke1
This is best, according to the engines, as Black threatened to prevent the king's escape with 27...Qf2.
27...Bc5 28.Qf5
White has stopped the mortal danger to his king, but Black has a second trump.
28...a3 29.Qxe5 a2 30.c4 e3 31.Nc1
The engines' best line is 31.Nc3 Qb2 32.Rxe3 Bxe3 33.Qxe3 a1=Q 34.Rxa1 Qxa1+ when Black is up a rook for a pawn.
The game finished:
31...Bd4 32.Qxb8+ Qxb8 33.Nxa2 Qf4 0-1

Champion Repertoire (part 10)

BORIS Spassky was 'only' world champion from 1969-72, but was an official candidate as recently as 1985.
A repertoire based on his games features many aggressive main lines, especially against the Sicilian and the French.
White
Open 1.e4 and meet the Sicilian: 1...c5 with Open lines, ie 2.Nf3, 3.d4 and (after 3...cxd4) 4.Nxd4 (Spassky is well-known for playing Closed variations with 2.Nc3, but he more often played the Open Sicilian and scored a higher percentage with it in ChessBase's 2020 Mega database).
He usually met the Najdorf: 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 with 6.Bg5, scoring 76%.
He also met 5...Nc6 with 6.Bg5, but tried six different moves in 15 games against 5...e6, winning all three times he chose 6.g4. He only faced 5...g6 six times, scoring 83% in three outings with 6.Be3 Bg7 7.f3 and the same percentage in three outings with 6.Be2 without an early f3.
In lines with 2...e6 3.d4 cxd4 4.Nxd4 he usually played 5.Nc3 against 4...a6, 4...Nc6 and 4...Nf6.
Games with 2...Nc6 normally transposed to lines already considered, but against 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e5 Spassky favoured 6.Ndb5 d6 7.Nd5 Nxd5 8.exd5 Nb8 9.c4.
Against 1...e5 he usually headed for a mainline Spanish: 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.0-0. After 5...Be7 he continued down the main line with 6.Re1 b5 7.Bb3 d6 8.c3 0-0 9.h3. If Black 'threatened' a Marshall Attack with 7...0-0, Spassky usually allowed it with 8.c3. Only two opponents in Mega20 went ahead with 8...d5, Spassky once accepting the gambit with 9.exd5 Nxd5 10.Nxe5 and once declining it with 10.d3!?
Against the Open Spanish: 5...Nxe4 he usually played 6.d4 b5 7.Bb3 d5 8.dxe5 Be6 9.c3.
Against the Steinitz Deferred: 4...d6 he liked 5.Bxc6+ bxc6 6.d4.
Against the Berlin: 3...Nf6 Spassky generally switched into a Spanish Four Knights with 4.Nc3.
Against the Schliemann: 3...f5 he normally played 4.Nc3, while against both 3...Nge7 and 3...Bc5 he preferred 4.c3, although the one time he faced 3...g6 he chose 4.d4.
Against the Petrov: 2...Nf6 Spassky liked Lasker's favourite, 2.Nxe5 d6 3.Nf3 Nxe4 5.Qe2 Qe7 6.d3 Nf6 7.Bg5.
Against the Philidor: 2...d6 3.d4 exd4 4.Nxd4 Nf6 5.Nc3 Be7 he liked to fianchetto with 6.g3.
Spassky usually met the French: 1...e6 2.d4 d5 with 3.Nc3, taking on the Winawer: 3...Bb4 with the mainline 4.e5 c5 5.a3 Bxc3+ 6.bxc3 and 7.Qg4.
Against the Classical: 3...Nf6 he liked 4.Bg5, usually meeting 4...Be7 with 5.e5 Nfd7 6.Bxe7 Qxe7 7.f4. If Black played the Burn: 4...dxe4 5.Nxe4 Be7 he played 6.Bxf6, and against the McCutcheon: 4...Bb4 Spassky's games went 5.e5 h6 6.Bd2 Bxc3 7.bxc3 Ne4 8.Qg4.
Against the Rubinstein: 3...dxe4 Spassky played 4.Nxe4, meeting the mainline 4...Nd7 5.Nf3 Ngf6 with 6.Nxf6+ Nxf6 (he apparently did not face 6...gxf6) 7.Bg5.
Against the Caro-Kann: 1...c6 2.d4 d5 he usually played main lines with 3.Nc3.
Against the Pirc: 1...d6 2.d4 Nf6 3.Nc3 g6 he usually played the Classical: 4.Nf3, but against the Modern: 2...g6 3.Nc3 Bg7 he very slightly preferred 4.f4, although every time he played 4.Nf3 the game transposed to a Pirc with 4...Nf6, which perhaps makes it a simpler repertoire choice.
Against the Scandinavian: 1...d5 2.exd5 with 2...Qxd5 he played main lines with 3.Nc3 and 4.d4 whether Black replied 3...Qa5, 3...Qd8 or 3...Qd6. Against 2...Nf6 he played 3.Bb5+ Bd7 4.Bc4.
Against Alekhine's: 1...Nf6 2.e5 Nd5 3.d4 d6 he had most success with the Four Pawns Attack: 4.c4 Nb6 5.f4.
Black v 1.e4
Aim for a mainline Closed Spanish: 1...e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.0-0 Be7 6.Re1 b5 7.Bb3 d6 8.c3 0-0 9.h3, and continue with the Breyer Variation: 9...Nb8. Play usually proceeds 10.d4 Nbd7 11.Nbd2 Bb7 12.Bc2 Re8 13.Nf1 Bf8 14.Ng3 g6 15.a4 c5 16.d5 c4 17.Bg5 (890 games reach this position in Mega20), and now Spassky usually played 17...h6 18.Be3 Nc5.
Naturally there are many sidelines along the way, but the main one is the Exchange Variation: 4.Bxc6. Spassky met this with 4...dxc6 and usually played 5...f6 against both 5.0-0 and 5.Nc3 (no games with 5.d4 in Mega20).
Against the Italian Game: 3.Bc4 he slightly more often chose 3...Nf6 rather than 3...Bc5, but scored 12 percentage points more with the latter. After 3...Bc5 he only met the Evans Gambit: 4.b4 once, declining it with 4...Bb6.
Against the Scotch: 3.d4 exd4 4.Nxd4 he definitely preferred 4...Bc5.
Against the Spanish Four Knights: 3.Nc3 Nf6 4.Bb5 he had most success with 4...Bb4, and against the Scotch Four Knights: 4.d4 exd4 5.Nxd4 he played 5...Bb4.
Against the Vienna: 2.Nc3 and the Bishop's Opening: 2.Bc4 he replied 2...Nf6.
Against the King's Gambit: 2.f4 he usually played 2...exf4, meeting 3.Bc4 with 3...Nf6, but against 3.Nf3, which he faced three times, he tried 3...d6, 3...d5 and 3...h6, winning all three games.
Black v 1.d4 and Others
After 1.d4 Nf6 2.c4 e6 he usually met 3.Nc3 with 3...Bb4 but against 3.Nf3 most often played 3...d5. In many of the Nimzo-Indian games he continued with 4...c5, while in the QGD games he usually met 4.Nc3, 4.g3 and 4.Bg5 with 4...Be7.
Against the English: 1.c4 he most often replied 1...e6, usually meeting 2.Nc3, 2.Nf3 and 2.g3 with 2...d5, although sometimes he played 2...Nf6 and then 3...d5.
Against 1.Nf3 Spassky most often replied 1...Nf6, usually transposing to lines already mentioned. If White went for King's Indian Attack set-up with 2.g3, he varied his response but had his best results with 2...d5 3.Bg2 c6.
He twice faced 1.b3, both times replying 1...e5 2.Bb2 Nc6.

Here is Spassky using his favourite weapon against the Najdorf in his second world championship match with Petrosian.
Spassky - Petrosian
World Championship (Moscow) 1969, Game 19
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6.Bg5
This is described as the main line in Wikipedia, although Julen Arizmendi and Javier Moreno in Mastering The Najdorf (Gambit 2004) call it The Old Main Line.
6...Nbd7!?
Much more popular is 6...e6, but the text is also often seen in grandmaster games.
7.Bc4!?
And here the main move is 7.f4, which is also the main move against 6...e6.
7...Qa5 8.Qd2 h6!?
Petrosian again avoids ...e6, which is overwhelmingly the normal move at this point.
9.Bxf6!? Nxf6 10.0-0-0
Spassky has given up the bishop-pair but has a sizeable lead in development.
10...e6
At last!
11.Rhe1 Be7 12.f4 0-0
Petrosian is the first to vary from Bruno Parma - Rajko Bogdanovic, Yugoslav Championship (Novi Sad) 1965. which continued 12...Qc5 13.Bb3 0-0 14.Kb1 Bd8?!, after which White got a strong attack with 15.g4!? Bb6 16.Qg2 (1-0, 33 moves).
13.Bb3 Re8 14.Kb1 Bf8
Petrosian keeps the dark-square bishop on the kingside to strengthen his king's defences, but Spassky nevertheless follows the general formula of Parma - Bogdanovic.
15.g4!? Nxg4!?
A bold decision that is liked by the analysis engines Stockfish11 and Komodo11.01, although even so both engines prefer White.
16.Qg2 Nf6 17.Rg1 Bd7 18.f5 Kh8 19.Rdf1 Qd8?!
This retreat was widely criticised, with grandmaster opinion at the time favouring 19...Qe5!?
20.fxe6 fxe6

White to make his 21st move

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21.e5!
Sacrificing a pawn to bring the queen's knight into the attack.
21...dxe5 22.Ne4 Nh5
Not 22...exd4? as 23.Nxf6 wins a piece since 23...gxf6? loses instantly to 24.Qg8#.
23.Qg6 exd4
Grandmaster Rainer Knaak in Mega20 gives one possible alternative as 23...Nf4 24.Rxf4! exf4 25.Nf3 Qb6 26.Rg5!! Bc6 27.Nf6 Be4 28.Qxh6+!!
24.Ng5 1-0
There is no defence, eg 24...hxg5 25.Qxh5+ Kg8 26.Qf7+ Kh8 27.Rf3 etc.
It is rare for a world champion to lose any game in 24 moves, never mind a game where his title was on the line, but that is the type of aggressive play Spassky was famous for in his heyday.