Bishop and Pawn vs Bishop: The Short Diagonal Wins
White to play and win
PlayBoth bishops are dark, and so is f8, so this time the promotion square can be defended. The pawn is stopped on f8 by two diagonals: a long one, and a short one only three squares long. With the move, your king reaches the good side and tips the balance.
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The Three-Square Diagonal
White to play and win · Win against perfect defense
Waking the engine…
The theory
In same-colored bishop endings with the defending king in place, the draw depends on the length of the bishop's diagonals. Four squares or more on both sides holds. A diagonal shorter than four can be lost, if the attacking king helps cover it.
Count the short diagonal. Here the pawn is stopped on f8, and the short diagonal f8-g7-h6 is only three squares. The bishop cannot hold three squares alone once the king pitches in.
Choose the good side. With the move, 1.Kg8 puts the king where it controls g7, a square of that short diagonal. Sent the other way, toward e8, the king controls none of it, and Black draws. That single tempo, and that single square, decide the game.
In this drill the defender clings to the long diagonal. Take the g8 side, force the bishop short, and push the pawn through.
Keep going
The Wrong Bishop
Black to play and draw
Centurini: Deflect, Then Interfere
White to play and win
The King Guards the Interference Square
Black to play and draw
All 24 bishop endgames positionsFollow the full curriculum (free)