Fundamentals (part 18)

Spanton (147) - Arthur F Reed (100)
Barbican (London) Rapidplay 1991

White has just captured on c4 - who stands better, and by how much?

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White has the more-centralised king and the better pawn-majority, so has an advantage. The opening, as you may well have guessed, was a Spanish Exchange, and a position like the one in the diagram is supposed to be White's dream ending. The supposition is probably correct, but Komodo10 reckons White has only a slight edge, while Stockfish10 is not that much more bullish about White's chances.
23...b6
The engines reckon Black should play 23...a5, although 24.f4, as in the game, and 24.b4, to get rid of White's doubled pawn (24...a4? is met by 25.b5), appear good answers.
24.f4 Kf7 25.e5!?
The engines strongly dislike this move, but it may be OK. They want White to gain queenside space with 35.b4.
25...fxe5
The engines switch their preferences between the text, 25...f5 and 25...Ke6, but it is not clear that any move solves Black's problems.
26.fxe5 Ke6 27.Kd4 c5+ 28.Ke4 b5
The engines prefer 28...g6, which covers the White king's entry square at f5, but they reckon White is much better.
29.c4 g5
Again the engines prefer ....g6, but with a large advantage for White.
30.g3 c6

White to play and win

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31.h4?
The only winning move is 31.h3, when Black will end up in zugzwang, eg if, as in the game, 31...h6 then 32.h4 gxh4 (32...b4 33.h5 a5 34.g4 etc, or 33...g4 34.Kf4 a5 35.Ke4 etc) 33.gxh4 and, once Black runs out of pawn moves, his king will have to retreat.
31...h6 32.h5 a5 33.cxb5?
This loses. White's easiest route to a draw is 33.g4 b4 34.Kf3 (or 34.Kd3) Kxe5 35.Ke3.
33...cxb5 34.g4 b4 35.Kd3 Kxe5 36.Ke3 Kd5 37.Kd3 a4?
This allows a draw. Black's most-direct win is 37...Ke5 38.Ke3 c4! 39.bxc4 a4 40.Kd3 a3 41.bxa3 bxa3 42.Kc3 a2 43.Kb2 Kd4 44.Kxa2 Kxc4 when Black wins both White's remaining pawns.
38.bxa4 c4+ 39.Kc2 Kc5

White to play and draw

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40.Kd2?
The drawing line is 40.b3 c3 (not 40...cxb3+? 41.Kxb3 and 42.Kxb4) when the mutual protected passed pawns mean neither side can make progress.
40...Kb6 41.Ke3
Black offered a draw.
41...Ka5 42.Kd4
I should have taken the draw as now it is Black to play and win.
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42....Kxa4?
This turns a win into a loss. Correct is 42...c3! 43.bxc3 b3 44.Kd3 Kxa4 etc.
43.Kxc4 b3
If 43...Ka5 then 44.b3.
44.Kc3
The game finished:
44...Kb5 45.Kxb3 Kc6 46.Kc4 Kb6 47.b4 Kc6 48.b5+ Kb6 49.Kb4 Kb7 50.Kc5 Kc7 51.b6+ Kb7 52.Kb5 Kb8 53.Kc6 Kc8 54.Kd6 Kb7 55.Ke6 Kxb6 56.Kf6 Kc5 57.Kg6 Kd5 58.Kxh6 1-0