Last time, I asked you how to refute a couple incorrect defensive tries for the opponent. The first one, 66.Kh6? was played in the game, leading to this position. The answer is below the diagram.
Solution
Black wins with 66…Nd3!, which was found in the game. The idea is that the king and knight will cooperate perfectly to chase the bishop away from controlling the f2 square. White’s only try is 67.Bh4, but then 67…Kg4! leaves the bishop no safe square that guards f2. That position deserves its own diagram.
Key Idea: The Short Diagonal
White’s problem is that his bishop was using the e1-h4 diagonal to protect f2. That diagonal is too short – only four squares. That allowed Black’s pieces to collectively take them all under control.
The other incorrect defensive try was 66.Bd2+?, leading to the following position.
Remember the principle at play here: Black needs to force the White bishop onto the short e1-h4 diagonal, so he can control all the squares and chase it away. Any move that allows Be3 is therefore incorrect. The bishop would reach the g1-a7 diagonal, with seven squares on it, and draw comfortably. This means that 66…Ke4! is the winning move, controlling e3. Then the bishop is forced back with 67.Be1, since otherwise the pawn queens. Black plays the familiar 67…Nd3, chasing the bishop away. White may respond 68.Bg3, bringing up the following position.
This wasn’t possible in previous lines, because the Black king was controlling this square. No matter: The king puts the white bishop in his crosshairs with 68…Kf5!. Now …Kg4 is unstoppable, with a familiar picture: The king and knight control all four squares on the short e1-h4 diagonal, and the pawn will be allowed to queen.
Key Ideas
1. In the fight between a passed pawn and a bishop, the defending bishop would rather control the pawn from a longer diagonal.
2. Without assistance from the defending king, the short diagonal (4 squares) allowed the enemy king and knight, working together, to attack the bishop and control all of the escape squares, allowing the pawn to promote.