Outsider vs. Majority

During the broadcast of my round one game in the last of the regularly scheduled Morning Membership tournament, Chris Bird highlighted the position of my game as another case where my opponent's outside passed pawn confers a winning advantage. However, I was confident that my position was better because of my pawn majority on the kingside. Later, during the last round, I commented in the chat that I had blown an elementary pawn ending in round one. I did indeed lose, allowing Chris to leave people convinced of his assessment.

However, the ending after the exchange of rooks was better for me, then an error gave me a lost position. My opponent threw away the win, and I blew it again. It was a typical blitz game. Chris's initial assessment that the outside passed pawn gave Black a decisive advantage was in error. My assessment that the ending was elementary might be a bit of a reach.

White to move

We have exchanged all four rooks on d8 to reach a pawn ending. White is one pawn ahead, but the pawn on b6 is doomed, which will lead to a pawn majority for White balanced by an outside passed pawn. I was confident that I should win this with White. In fact, with best play by both sides, the game should probably be drawn.

34.Kf2 Kd7 35.Ke3 Kc6 36.Kd4 Kxb6

White to move

37.g4??

37.Kd5 Kc7 38.Kc5 b6+ 39.Kd5 Kd7 looked equal to me because it is.

37.f4 was playable

37...Kc7??

37...g5-+

38.f4 Kd6 39.h4??

39.e5+ Kd7 (39...Ke6?? 40.f5++-)

39...Ke6

39...f6-+

40.e5 b6??

40...g6 is equal.

White to move

Practice Position

Convinced that I had a winning position here, I played multiple games against Stockfish on my iPad the next morning. I manged to find one way to lose, and several winning variations. I also found the position had enough complexity that most of my battles against the engine ended as a draw. As this was a blitz game, I played quickly against Stockfish.

Stockfish on the iPad plays a little weaker than other versions and blundered at least once. After studying the variations, I played against Stockfish, Komodo, and Fritz 13 on my laptop. I won every game easily.

Here I blundered in the game.

41.Kc4??

41.f5+ should have been easy to find. See below for the critical variations.

41...b5+??

41...g6-+
41...h5-+

42.Kxb5 Kd5 43.h5 Ke4 44.g5 hxg5

White to move

45.fxg5??

45.e6 fxe6 46.fxg5=

My opponent won easily from here.

Proving Games

From the diagram labeled "Practice Position" above, White is clearly better after 41.f5+. I played this move against Stockfish in several games the next morning. Below, I present the key variations from these games. This morning's battle with Fritz 13 is an interesting place to begin.

41.f5+ Ke7 42.Kd5 g6 43.f6+ Kd7 44.g5 h5

White to move

In battles with the engines, I reached this position via several move orders. Against Stockfish on Tuesday I struggled, finding only a draw. 

45.e6+!

This move creates a passed pawn for White and ties down Black's king.

45...fxe6+ 46.Ke5 b5 47.Kd4 Kd6 48.Kc3 e5

White to move

49.Kb4 e4 50.Kc3 Ke6 51.Kd4 Kd7 52.Kxe4 Ke6 53.Kd4 b4 54.Kc4 Kf7 55.Kxb4 Ke8 56.Kc5 Kf8

White to move

57.f7! Ke7 58.Kd5 Kxf7 59.Kd6 Kf8 and the rest is an elementary opposition and outflanking exercise.

What if Black plays 41...Kd7? White goes after the b-pawn. 42.Kc4 Kc6

White to move

43.g5!

a) 43...h5 44.f6

Black to move

44...gxf6

44...g6 is similar to the game against Fritz, except that Black's king has left his defensive post. 45.e6 b5+ 46.Kd4 b4 47.exf7.

45.exf6 Kd7 Kb5

b) 43...b5+ 44.Kb4 hxg5 45.hxg5 Kd5

White to move

We have reached a breakthrough exercise identical in its essential aspects to one I presented to my students several months ago. Perhaps it is in a textbook somewhere.

46.e6 fxe6 47.f6 gxf6 48.g6

Black to move

White wins.

In every variation, basic techniques of opposition and outflanking, breakthrough, and understanding of the square of the pawn come into play. With correct play after 40...b6, my majority was dominant. Because of incorrect play on my part, my opponent's outside passed pawn prevailed. I had pursued what I thought was a winning pawn ending through the middlegame, but my majority was balanced by my opponent's outside passed pawn, and the game should have been a draw.