The pawn too many

White wins White to move · Endgame principles · Difficulty about Elo 1900

The plan

An extra pawn is almost always an advantage — here it is the difference between a full point and a half point, and in the wrong direction. The position is won with a single move: the rook goes to the a-file and gives check. The black king stands in the corner, its own rook is the only defence, and after the forced block on a6 it is simply captured — mate. Now the counter-test, measured: give White a SECOND pawn, of all places on the square the rook needs to check from, and the very same position is only a draw. The extra pawn takes away the square the rook's own piece needs to win, and no other move replaces it. You can even see this in the winning position itself: whoever moves the pawn instead of the rook and puts it on this square throws the point away on the spot.

Rule of thumb: don't just count material — check which SQUARES your own pawns occupy; a pawn on the wrong square is a piece taken out of play.

Why this level: An extra pawn that costs the win — pure judgement

The solution, move by move

1. 1. Ra4+ The ONLY winning move out of seventeen. The rook builds the mating net with a single check, because the black king in the corner has no air: the white king covers b7 and b8, and the rook now takes a7 away from it. And this exact square, a4, would be occupied by a second white pawn — then this move would not exist, and the position would be a draw.
   Sideline 1. a4 The proof of the point: the pawn itself marches onto the square the rook would have needed. Win becomes draw in a single move — and all White did was push a pawn forward. 1… Rh7+ From now on the black rook checks from behind, and White never gets the chance to build the mating net. 2. Kb6 Rb7+ The king is driven away by its own pawn. This is exactly how the position with two pawns runs from the very start: a draw.
   Sideline 1. Rc6 Standing in for every other rook move: it looks active but gives the black rook time for checks from behind. 1… Rh7+ The rook gets behind the white king and drives it away. Without its king the white rook no longer has a mating net. 2. Kb6 Rb7+ 3. Ka5 Rb1 The rook keeps its distance and just keeps checking forever. A draw, even though White has an extra pawn.
   Sideline 1. Rh4 And for completeness, the one real catastrophe: the rook places itself in front of the enemy rook. 1… Rxh4 Rook gone. A single pawn no longer wins here.
2. 1… Ra6 The only legal move. The king cannot go anywhere, so the rook has to throw itself onto the file.
3. 2. Rxa6# Captured, mate. Two moves — with an extra pawn on a4 it would have taken infinitely many.

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