Derived from Alekhine

Alexander Alekhine gave a cute checkmate idea that did not occur in his game with Arthur West, Portsmouth 1923.*

The hypothetical position makes a good puzzle, except that there are two ways to achieve checkmate in four moves. Sergey Ivashchenko improved the puzzle by removing a pawn and shifting Black's rook one square to the left. Alekhine's solution remains mate in four, but the alternate idea now takes five moves. Encountering Ivashchenko's puzzle in The Manual of Chess Combinations, vol. 2, no. 65 this morning, I chose the alternate idea, failing the puzzle (I gave myself half-credit).

White to move

The game reached this position after 27 moves.

White to move

28.Bxd5 was played.

28.Bd1 Nb4 leads to the position where White has two ways to force checkmate.

White to move

Analysis diagram

28...exd5

Black needed to address the threats to his king instead of capturing the bishop, but even then his game is lost.

29.Nf6+ and Black resigned.

What was the idea that Alekhine rejected?


*I do not know where Alekhine discussed this game. My source is a comment on the game by Sally Simpson on chessgames.com.