Sunday, August 8, 2021

Season 21 superfinal games 81-90

After 90 games Stockfish leads 15-6 with 69 draws. For the first time in the superfinal there were 3 game pairs which were biased in favor of black. Stockfish won two game pairs, its lead is now 9 points. Leela probably missed a win in one game. Leela's chances of catching up are purely theoretical with 10 more games to play.

In game 81 there was only one pawn trade after the start, the center was blocked and there was one open file on the queen side. Stockfish moved a rook forward on the king side, its king walked there without castling. Evals came down and the engines started to shuffle on move 25. There were no weak spots to attack, the game was adjudicated on move 59. Game 82 started similarly, this time Leela moved its queen forward on the queen side and grabbed a pawn. Stockfish trapped the queen and eventually Leela gave the queen for a bishop and a rook. Evals were close to 0, the engines reduced to a Q vs RB ending and the game was adjudicated after the pawn captured stopped.

Games 83-84 started with a King's Gambit Accepted, Kieseritzky gambit Berlin defense. In game 83 there was only one pawn exchange after the start. Leela diverged from the known line, after the pawns stabilized Leela castled long. Stockfish gave a knight for two pawns and opened the queen side. The engines played out a long PV agreement, evals came down and the game reached a RRN vs Q imbalance on move 30. Stockfish was 4 pawns up with 3 connected passers on the king side, but Leela used its pieces to block the black passers and the game was adjudicated early on move 38. In game 84 there were more minor piece exchanges after the start and Stockifsh castled short. Stockfish opened the queen side and moved a rook forward. The engines exchanged a pair of rooks and the white queen moved forward. The engines started to shuffle and evals came slowly down. There were a few pawn moves and piece exchanges, on move 71 the game reached a RB vs RB position. Leela wouldn't lower its eval, the game was finally adjudicated on move 112.

Games 85-86 started in the English symmetrical variation, a line where black gives a knight for two pawns, creating connected passers on the queen side, while white offers a rook. In both games black took the rook. In game 85 Stockfish walked its king to the king side and pushed the passers on the queen side. Leela pushed pawns on the king side, it thought long on a few moves but couldn't find a way out, evals kept increasing. One black passer reached the 3rd rank, Leela used pieces to block. 

Leela opened the king side with its pawns, but it didn't have the strength for an attack on the black king. Stockfish gave back a rook for a knight and created a 3rd passer on the queen side, then pushed it all the way to the 2nd rank.

Leela could only defend, Stockfish was on its way to win but it was still far. The black queen came forward, then Stockfish gave a rook for two pawns and removed any danger to its king. Stockfish attacked the black king with its queen and bishop, Leela managed to capture two passers on the queen side but Stockfish used checks to capture almost all the white pieces, with mate following. Incredibly, the black knight on g8 never moved in the game.

In game 86 the black queen came forward and Leela traded it for a bishop and knight. Stockfish gave a rook for a bishop and captured one black passer on the queen side, evals started to come down. The engines reduced to a QB vs RRN position on move 28 and Stockfish captured the remaining passers, clearing all pawns on the queen side. After a few pawns trades the engines started to shuffle, Leela wouldn't lower its eval enough for 5 straight moves and the game was adjudicated only on move 93. Stockfish wins the game pair, it leads 14-6.

Games 87-88 started with a Sicilian dragon, Yugoslav attack. In both games the engines castled in opposite directions. In game 87 Stockfish pushed pawns and opened the queen side, Leela pushed a pawn to h6. Evals kept increasing as Leela prepared to open the king side. On move 27 Leela pushed f4 and Stockfish took it with a pawn, Leela naturally took back with its queen and immediately Stockfish's eval dropped. Leela thought for 13 minutes and its eval dropped as well. I don't really understand what Leela missed, the engines continued with a long PV agreement and exchanged most pieces. On move 39 the game reached a RB vs RB position, evals were close to 0 and the game was adjudicated. This seems like a missed win by Leela.

In game 88 Leela pushed pawns on the queen side and Stockfish captured one. Stockfish did not push pawns on the king side, it concentrated its pieces on the queen side. Evals increased slowly, Leela threatened the b2 pawn with all its major pieces but Stockfish's defense was sufficient. Stockfish turned to the king side, it gave back the pawn and opened a file on move 34. The white queen came forward and exposed the black king, Leela tried to exchange pieces but Stockfish was determined to avoid this.

Stockfish had a clear advantage in the open position, its king was safe in the corner while the black king was exposed and in danger. After exchanging a pair of rooks Stockfish attacked with its queen and rook, Leela was under constant threat of mate. On move 62 the remaining rooks were exchanged, evals were over 11 by then.

Stockfish quickly captured the two black pawns, Leela chose to give up its queen and be mated, rather than to delay the loss or reach a tablebase position. Stockfish wins the game pair, it leads 15-6. 

In game 89 there were no exchanges after the start and evals came down. On move 19 the engines opened a file on the king side, then Stockfish captured a pawn on the queen side. After some shuffling the engines opened the queen side and Leela regained the pawn. Leela had a passer on the queen side but evals were close to 0. Leela captured a pawn on the king side and created a second passer, Stockfish gave a rook for a knight and pawn to create two central passers, then attacked the white king. Leela offered the exchange back, Stockfish preferred to capture the king side passer. The pawns stopped moving and the game was adjudicated.  In game 90 there was one pawn trade after the start without opening a file. The engines developed behind the pawn lines and exchanged minor pieces. On move 32 there were no  knights on the board, Stockfish's eval was over 1 but all it could do was shuffle. A few pawn moves extended the game, adjudication came finally on move 114.


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