Memorable Finish

MY performance at this year's Gibraltar congress was mostly memorable for all the wrong reasons.
I played in the U1900 morning tournaments, Amateurs A (Jan 22-26) and B (Jan 27-31).
My scores of +1=3-1 and +2=1-2 were enough to lose 18 and 24.6 Fide elo.
The following game, one of my three wins, was memorable for a better reason, at least for me. There are some instructive moments during the game, and a sudden finish that is well worth memorising if you have not seen the idea before.
Brian Izzard (1657) - Spanton (1888)
Gibraltar U1900 B (Rd 4), 2018
1.d4 d5 2.Bg5
The game starts as a Pseudo-Trompowsky ...
2...Nf6 3.e3 Nc6 4.Nf3
... morphs into a Torre Attack ...
4...Bg4
... and becomes, at least from Black's viewpoint, a Pseudo-Chigorin.
5.Be2 e6 6.Nbd2 h6 7.Bh4 Be7 8.h3 Bf5 9.Bb5
Black was threatening to win a pawn, which I thought explained this move. However, after ...
9...a6
... instead of playing Bxc6, Ba4 or Bd3, White chose ...
10.Be2?
The game continued ...
10...Nb4 11.0-0
11.Rc1? Nxa2 is no improvement.
11...Nxc2?
The wrong capture. Correct was 11...Bxc2, forcing White to spend a tempo moving his queen.
12.Rc1 Nb4

Position after Black's 12th move

I had seen that 13.Bg3 was simply met by 13...Nc6. However, it was only after moving that I saw White had ...
13.Qb3
Then came ...
13...Bd6
I played this partly to set a trap that White eventually falls into. The key point is that the bishop protects c7.
But better was 13...a5! and if 14.a3, then 14...a4 15.Qd1 Nd3.
It turns out that 13.Qb3 was not the best move. Instead, Stockfish8 gives 13.Ne5! getting ready to capture twice on c6 after Black's knight on b4 is forced to retreat.
14.Ne5 g5 15.Bg3 0-0
I could see nothing better than to give back the pawn.
16.f4
White is in no hurry to restore material equality. Instead, he hopes to open lines against Black's weakened king.
16...Ne4
Stockfish8 prefers 16...Rb8, but I did not have much faith in Black's resulting passivity.
17.Nxe4 Bxe4 18.a3 Nc6
White has two ways to regain the pawn.
In the post-mortem we looked at lines such as 19.Nxc6 bxc6 20.Rxc6 Rb8 21.Qc3 Rb6 22.Rxb6 cxb6 23.Bxa6, when Black has gone from a pawn up to a pawn down.
Stockfish8 prefers to go a pawn down by 20...Qd7 21.Rxa6 Rxa6 22.Bxa6 c5,when it reckons Black's activity and better piece-coordination give full compensation for the material deficit.
In the game, White chose ...
19.Qxb7??

Black to play and force immediate resignation

19...Na5 0-1