Queen against two bishops — won, but not within fifty moves

White wins White to move · Queen endgames · Difficulty about Elo 2000

The plan

Queen against two bishops is almost always won — but it is the material case where the fifty-move rule really bites. The tablebases know the difference between 'won' and 'won within the rule', and here the two gaps widen far apart. Measured over random positions, only about one in seventy is even such a borderline case at all — but if the bishops stand by their own king, where they belong, it is already one in sixteen, and once you are stuck in one, it is inescapable. In the starting position there is exactly one move that brings the win home in time; it needs eleven half-moves to the first capture. Eighteen other moves also win — but only after more than a hundred half-moves, and on the board that means: a draw. The path itself is a check series that drives the enemy king away from its bishops until one of the two stands undefended. Equally important is what you must NOT do: against two bishops all the diagonals are mined, and a single move onto the wrong square costs the queen. Whoever has this position as the defender plays it the other way round — keep the bishops together, drag out the moves, watch the clock and the count.

Rule of thumb: against two bishops, won does not equal won — only the path that quickly leads to the first capture counts.

Why this level: Won, but not within fifty moves — rule knowledge needed

The solution, move by move

1. 1. Qf7+ The ONLY move that wins within the fifty-move rule — out of thirty. Eighteen alternatives also win in theory, but need more than a hundred half-moves to the first capture and are therefore a draw on the board. Two king moves are even a genuine draw, and nine queen moves lose the queen to a bishop (first sideline).
   Sideline 1. Qd5 The queen centralises and attacks the bishop — on a square the other bishop guards. 1… Bxd5 Gone. Against two bishops you have to check both diagonals before every queen move, not just one.
   Sideline 1. Kg4 Bring up your own king first — the idea is correct in many endgames and wrong here. 1… Bc8 The ONLY move that saves Black: the bishop places itself in front of the queen and offers itself. 2. Qxc8+ Kxc8 King and bishop alone do not mate — a draw. A single loss of tempo has turned the win into a draw.
2. 1… Kb8 The king has to go into the corner; every square is equally bad.
3. 2. Qf6 A quiet move: the queen places itself so that both bishops lie within its reach.
4. 2… Ba8 The bishop seeks safety in the corner — and stands there permanently out of the game.
5. 3. Qd8+ Now the hunt begins. Every check drives the king one square further away from its pieces.
6. 3… Kb7
7. 4. Qd5+
8. 4… Kb8
9. 5. Qb3+ The key check: it hits the king and attacks the second bishop at the same time.
10. 5… Kc8 The king has to get out of check and leaves the bishop alone.
11. 6. Qxa3 The bishop falls, and the count for the fifty-move rule starts over. Queen against one bishop is a clean win.

More in Queen endgames

• Perpetual check — the only rescue for the weaker side Draw
• Queen against two knights — the king step decides White wins
• Queen and pawn against queen — the knight pawn jams Draw
• Queen against rook and bishop — both on a knife's edge Draw
• Queen and pawn against queen — the rook pawn isn't enough Draw
• Perpetual check or mate — the king marches behind the queen White wins