Wednesday, February 20, 2019

Season 14 superfinal, games 71-80

After 80 games Stockfish evens the score to 9-9 with 62 draws.
There were 9 draws, in which Leela had 2-4 missed opportunities to win. Then came game 80, a spectacular game. Leela's evaluation was misleading and Stockfish won with two white queens on the board.

There were almost no exchanges in the first 35 moves of game 71. The center and queen side were blocked by pawn lines, Leela concentrated forces on the king side and its eval steadily increased. Stockfish's king ran to the queen side as Leela opened the g file and white pieces moved forward into black territory. Leela's eval peaked over 5, Stockfish also thought it was in trouble with an eval over 2.

Leela's attack seemed to lose steam at this point. The white pieces couldn't attack from the king side, the white king was exposed and Stockfish threatened to attack with its queen. Leela gave a rook for a bishop and got a passer to the 7th rank, Stockfish blocked with a rook and its eval dropped to 0. Leela's attack was over and the game was adjudicated 20 moves later. Was this another missed chance for Leela?

In the reverse game 72 there were more exchanges and the position was open. Evals started around 1 and gradually came down, despite the fact that Leela gave a rook for a knight. Leela had two forward knights near the white king that looked intimidating. In a series of exchanges the game reached a Q vs QN position, Leela 3 pawns up. Stockfish exchanged queens and was in time to stop the white pawns with its knight, resulting in a draw.

There were many early exchanges in game 73, only QBN vs QBB were left on move 26. Leela had a queen side passer, Stockfish's eval was 0. The engines reduced to a queen ending and Stockfish gave checks for almost 50 moves. The game was adjudicated when Leela lowered its eval enough for the draw rule. In game 74 Stockfish was up a pawn with a queen side passer and eval above 1. Leela created a pawn line across the board and the engines started to shuffle from move 22. After about 50 moves there were several exchanges and evals came down, then the engines resumed shuffling. The game ended in a draw by the 50-move rule.

In game 75 evals didn't move a lot after the opening. By move 25 the engines cleared two files on the queen side, all pieces were still on the board. The center was locked, then all rooks and queens were exchanged off by move 35. Evals started to increase slowly though material was equal, Leela's eval reached over 2 and stayed there for another 20 moves. Then Leela pushed pawns on the king side and its eval jumped over 4.5.

Leela had a bishop pair and a queen side passer, Stockfish's pieces had very little space. However, Leela seemed to have no plan how to continue and the engines shuffled for 30 moves, Leela's eval slowly decreasing. The engines cleared the king side pawns and Stockfish's eval dropped. The black bishop was free to move, Leela's advantage was over. The game continued until reaching a tablebase draw on move 159.

There were more early exchanges in game 76, and several minor pieces were off. Stockfish attacked on the king side but wasn't strong enough. Leela gave a pawn in the center and evals came down. Mostly major pieces remained, Leela covered the back ranks and didn't allow the white pieces to get there. The position stabilized and the game was adjudicated by the draw rule.

Games 77-78 started with a 23-ply book sequence in the Benoni Defense. There were many early exchanges in game 77, only QRR vs QRN remained on move 21. Stockfish was two pawns up and its eval was 0. The engines shuffled for a while when Stockfish's eval jumped over 2, it was convinced Leela had an advantage. This lasted for a few moves, then Leela exchanged a pair of rooks and opened the king side, Stockfish's eval fell back to 0. Leela's king was exposed and Stockfish had a perpetual check draw. Leela agreed to the draw on move 117. In game 78 there were only a few exchanges. Stockfish's eval stayed around 1, Leela blocked the board with a pawn line and the engines started to shuffle on move 33. Leela had a central knight that attacked two weak white pawns, forcing Stockfish to keep a defending piece for both. After 30 moves Stockfish opened a file on the king side, and for a brief moment its eval jumped close to 2. Leela remained calm despite being low on time, it captured a pawn on the queen side and evals fell immediately down to 0. Stockfish couldn't attack when it had to keep an eye on the black queen side passers. The engines shuffled and exchanged pieces until adjudication on move 149.

The position was closed in game 79 with very few exchanges. Leela had a space advantage, its eval was over 1 and it increased slowly. The queen side was blocked, Leela had a knight pair which is better in closed positions, Leela's eval went over 2.5. The engines shuffled pieces and pushed pawns on the king side until it was also locked. On move 90 Stockfish gave a rook for a knight and the engines continued to shuffle with evals coming down. On move 140 Leela traded its other knight and gave up its advantage. The game was adjudicated on move 191.

In game 80 the position was again closed. Stockfish had a space advantage and eval over 1, it preferred trading a knight for a bishop so Leela had the knight pair. Stockfish pushed pawns on the king side, Leela blocked with its pawns. Evals started to increase when Stockfish gave a knight for pawns and broke through the center. Stockfish followed with a knight for rook trade and its eval jumped over 3.

After exf7+ Leela moved its king to h7, assuming that Stockfish would take the knight, more or less equalizing material. Stockfish however chose to promote on f8, safe because of the pinned bishop. This cost a white rook but now Stockfish had an unusual 2 queens. Stockfish's eval shot up, Leela was incredibly cool.

Leela's eval started to react to the situation only on move 47, much too late. Stockfish's queens dominated the board and Leela couldn't stop them. The game ended with mate a few moves away. An incredible game, quite unexpected behavior by Leela. Stockfish wins the game pair and evens the score of the match.

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