The queen skewer — curse of the long diagonal

White wins White to move · Pawn endgames · Difficulty about Elo 1200

The plan

Rook pawn against rook pawn, both queen — and White still wins. The reason is pure geometry: the two queening squares a8 and h1 lie on the SAME diagonal, and the black king stands right in the middle of it. The white queen appears with check, the king has to step aside — and behind it the brand-new black queen hangs on the skewer. How exactly this position is built is shown by the measurement: of the eight moves in the starting position exactly ONE wins, and the other seven cost not merely half a point but the whole game. It stays that way to the end, because every further white move of the solution is likewise the only one that holds the win — four out of four. That it really is the diagonal that decides, and not the pawn count, is shown most clearly by the counter-test: leaving everything else in place and putting the black king in turn on every other square, White wins nowhere else — of 52 possible squares, e4 is the only one that wins, four are drawn, and on 47 White actually loses. One square over, and the whole point turns into a whole loss.

Rule of thumb: in rook-pawn races always check the long diagonal first — whoever's king stands on it loses his queen the moment she is born.

Why this level: The skewer after promotion — tactics already in the endgame

The solution, move by move

1. 1. a6 Only the pawn wins — measured, one of eight moves, and the other seven actually lose. 1.Kf6?, for instance, lets Black step into the square of the a-pawn with Kd5! (sideline).
   Sideline 1. Kf6 The king has no business on the queenside: 1… Kd5 Into the square! From d5 Black catches the a-pawn — 2. a6 Kc6 The only move that keeps hold of the win: the king stays inside the square and goes to meet the pawn. 3. a7 Kb7 — the pawn is stopped, and on the other wing the h-pawn runs unhindered to the queen: White actually loses. 4. a8=Q+ Kxa8 Even the desperado sacrifice changes nothing — the h-pawn runs through. 5. Ke5 h2 6. Kd4 h1=Q
2. 1… h2
3. 2. a7 Again the only winning move among eight: the pawn runs, the king does not stir. Both sides are racing — and White cannot afford to waste a single tempo.
4. 2… h1=Q Black has reached queening in time — or so it seems. Because his king stands on the a8-h1 diagonal, the unlucky one.
5. 3. a8=Q+ With CHECK, and again as the only move of eight. The king must clear the diagonal —
6. 3… Kd3
7. 4. Qxh1 — and the queen is gone: the skewer on the long diagonal has decided the race. This capture too is the only winning move, here among 26 possible ones.

More in Pawn endgames

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• The trebuchet — whoever moves loses White wins
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• Key squares — the sixth rank always wins White wins
• The doubled pawn as a tempo reserve White wins