Saturday, February 6, 2021

Season 20 superfinal games 81-90

After 90 games Stockfish leads 11-5 with 74 draws. Stockfish won 3 more game pairs, making it 6 wins in the last 10 game pairs. With 10 games to go Stockfish is going to win the match, Leela needs a miracle to make a late comeback.

In game 81 there were no exchanges after the start, Leela pushed pawns on the king side and Stockfish pushed pawns on the queen side. Stockfish's eval went over 1 as it opened the queen side, went a pawn up and created a passer. The first pieces were exchanged on move 30, Stockfish supported its passer from behind and Leela doubled rooks on the file. The passer moved to the 5th rank and the engines exchanged queens, then started to shuffle. After a while Stockfish lowered its eval and the game was adjudicated. In game 82 Leela opened a file on the queen side and the engines exchanged a pair of rooks. The king side opened and evals came down, the engines reduced to a QN vs QB position. The white king came forward and Leela gave the knight for pawns, the game was adjudicated when the pawns stopped moving.

Games 83-84 started with a 20-ply book in the Sicilian Dragon, Yugoslav attack, where the engines castled in opposite directions. In game 83 queens were off early, Stockfish gave a knight for 2 pawns, forcing the black king to move and creating an advanced passer in the center. Leela lost a bishop for the passer and the engines reduced to a RB vs RB position with Stockfish a pawn up. After exchanging rooks the game reached an opposite bishop ending, Stockfish's eval kept the game going until move 186. In game 84 queens were also off early, the engines locked the queen side and evals came down. The center opened and after several exchanges the game reached a N vs B ending. Leela lowered its eval after 45 shuffling moves and the game was adjudicated.

In game 85 Stockfish's eval was over 1 from the start. Stockfish threatened the king side, Leela used its pawns to push the white queen back and exchange queens. Stockfish went a pawn up and its eval increased steadily. It was over 2.5 after Leela gave two more pawns and traded a rook for a bishop and a knight in a long PV agreement.

The exchanges continued and the game reached a R vs BN ending on move 33. Stockfish's eval was over 3 and climbing, Leela's eval did not change and drifted down if anything. From move 38 Leela started to think hard, more than 10 minutes per move, and its eval went over 1. The engines traded pawns until only 3 white pawns and one black were left.

The endgame was very long, Leela's eval started to react on move 46. By move 56 the engines traded a pair of pawns. Leela did not want to capture a white pawn to avoid a 6-man tablebase win, Stockfish queened the other pawn and the game was over.

In game 86 Stockfish locked the center and the queens stayed on the board. Leela didn't attack the king side immediately, it gave a pawn on the queen side and opened a file. The white king walked to the center and Leela pushed pawns on the king side. Leela had a strong DS bishop and evals were around 1.5, but the engines mostly shuffled. On move 62 Leela captured a pawn and equalized material, evals went over 2 and shuffling resumed. Leela did not have a plan, the engines opened another file on the queen side, pawn moves and exchanges extended the game to move 157. Leela traded Q for RN, 40 moves later it finally lowered its eval, the game ended in a repetition. Stockfish wins the game pair, it leads 9-5.

In game 87 Stockfish considered Leela's move 7 as a blunder and its eval jumped to 1.5. The engines played out a long PV agreement in which the black queen came forward to capture a pawn and Stockfish captured a rook for a knight. Evals did not change much through this move sequence.


There was another long agreement in the PV, Stockfish forced a bishop exchange and then the engines shuffled for a while. Stockfish's eval started to increase after Leela pushed a pawn on the king side. With the new pawn structure Leela's king became vulnerable on the back ranks. Both evals increased, the engines exchanged queens and only RRB vs RNN remained.

The material difference was enough to give Stockfish the win. The engines continued to trade pieces and pawns until the game ended in a tablebase position.

In game 88 Leela gave a pawn and opened a file in the center. There were many early exchanges including the queens. Leela had a bishop pair advantage and it avoided exchanging bishops. Evals were over 1 for a while, Stockfish's queen side knight was still on b8, yet Leela could not find a weakness or a way to break through. After move 38 Leela exchanged both its bishops for a rook and the black knight that finally moved. The engines shuffled and evals slowly came down, on move 115 Leela gave the material back and reduced to a drawn rook ending. The game ended in a tablebase draw. Stockfish wins another game pair, it leads 10-5.

In game 89 the engines opened a file in the center and Stockfish gave a pawn. Stockfish's eval was over 1 but it remained more or less constant. Stockfish pushed pawns on the king side until it stabilized, then the focus turned to the center. Stockfish regained the pawn, the all the bishops were exchanged. On move 30 Stockfish took back a bishop, though this was the obvious move expected by both engines its eval jumped to 2.

Stockfish's PV predicted the next sequence of moves, its eval increased steadily and before long Leela's eval started to react as well. Stockfish targeted the black knight, using various pins to make sure it doesn't move. Stockfish gave two pawns to get rid of the e6 pawn, then it reduced to a RN vs R position.

The endgame was slow, Stockfish played patiently. First to go was the black f pawn, Leela tried to push the h pawn but after exchanging rooks Stockfish captured it too. The game ended in a tablebase win.

Game 90 followed the previous game, Stockfish was a pawn up and there was an open file in the center. Leela pushed pawns on the king side, this time the pieces stayed on the board longer and evals came down. Leela gave a second pawn, then opened a file on the king side and threatened the black king but Stockfish felt completely safe. The engines exchanged a pair of rooks and Leela moved a rook to the 8th rank. When the white queen came forward Stockfish ended the game in perpetual check. Stockfish wins a third consecutive game pair and it leads 11-5.


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