After 90 games Stockfish leads 23-8 with 59 draws. Stockfish added two more game pair wins, increasing its lead to 15, not so far from last season's gap of 19 against KomodoDragon. Opening bias continues to be high, there were two game pairs with two white wins. One of these was the highlight of the match for me, crazy game 88. In terms of eval it seemed like an easy win for Stockfish, but the game itself, at least the middle game, was quite mad: including a declined queen offer and a rook hanging for 10 straight moves.
Games 81-82 started in the Alekhine defence, four pawns attack, played in high level human chess. In game 81 the engines opened the center files and queens were off early. Both kings moved forward without castling, the engines opened the h file and exchanged a pair of rooks. Evals came down and the engines shuffled and exchanged pieces. The game reached a knight ending, there were too many pawns for the draw rule, the game was adjudicated on move 84. In game 84 both engines castled short and queens stayed on the board. In a long PV agreement the engines opened the d and f files and exchanged a pair of rooks. Evals came down as the engines exchanged pieces, in a QRB vs QRB position Leela captured a pawn and its eval dropped to 0. The white queen came forward to attack the black king, Stockfish captured a rook for a bishop and the game reached a R vs B ending. Stockfish thought it had an advantage and wouldn't lower its eval. Pawn moves extended the game, it was adjudicated only on move 145.
Games 83-84 started with a 24-ply book in the KID orthodox, bayonet attack, played in high level human chess. In game 83 a series of exchanges opened the position after the start and evals came down. The engines continued to exchange pieces, Stockfish went a pawn up and the game reached a QB vs QB position. Evals were low but there one pawn too many for the draw rule, the game was adjudicated on move 90.
In game 84 the center remained locked, there were a few exchanges after the start and the position remained closed, only one file was opened on the queen side. Stockfish's eval started to increase while Leela's eval decreased, On move 28 Stockfish captured a pawn on the king side with a bishop, Leela blocked the bishop's way back but its eval jumped. The black king was exposed with the g and h files half-open, Leela added pieces to defend it and Stockfish used the time to capture another pawn.
Stockfish moved a rook forward and exchanged a pair of rooks, it then pushed its central passer to the 7th rank and Leela captured it. There was a lot of pressure on the e5 pawn, with 3 pieces attacking it and 3 defending. In a PV agreement the engines traded Q for RNN.
The position looked difficult but not for engines. After trading pawns and bishops Stockfish's target was the a7 pawn. It kept its pieces safe, protecting each other when possible. Leela tried to split them with its queen but Stockfish always had a tactic even when a piece was hanging. Eventually Stockfish captured the a7 pawn safely, Leela couldn't prevent a queening and mate. Stockfish wins the game pair, it leads 20-6
Game 85-86 started with a 14-ply book in the Caro-Kann advance variation, played in high level human chess. In game 85 Leela pushed pawns on both sides and opened the 3rd rank. Stockfish castled short and evals started to increase. After a few pawn exchanges the king side opened and Leela used the open 3rd rank to move its queen to the king side quickly. While Stockfish added pieces to defend its king Leela captured a pawn and created a central passer.
Both kings were exposed but Stockfish was too busy defending and had no time or resources for an attack. The engines exchanged a pair of rooks and then queens. In a RBN vs RBN position Leela moved its rook forward and captured a second pawn. Both engines had a passer on the e file, Stockfish gave a knight to capture the white passer, it pushed its passer to the 2nd rank.
The white king moved to replace the bishop as a blocking piece. After exchanging bishops Stockfish could not protect its passer and Leela captured it. Stockfish lost more material and was mated.
In game 86 evals were stable after the start, Stockfish pushed pawns on both sides and there were a few exchanges. Leela created a central passer through a bishop exchange, the passer was isolated and behind the white pawns. Leela opened the c file and moved a rook and a bishop forward trying to disrupt the white pieces, but evals started to increase. On move 25 Leela protected its passer and offered a knight.
Stockfish didn't take the knight to avoid getting the black queen involved. In a long PV agreement Stockfish captured the passer and moved its queen forward, capturing another pawn in the center. Leela gave a rook for a bishop and exchanged queens, the game reached a RR vs RB position with black a pawn up.
The ending was very slow. After trading pawns each engine was left with one pawn in an 8-man position. The black bishop protected the black pawn, Stockfish kept the black king on the queen side and Leela had only the rook to defend against the white passer. Stockfish slowly pushed its passer forward delayed by checks, eventually it queened and mated. There were two white wins in this game pair, Stockfish leads 21-7.
Games 87-88 started in a rare sideline of the French defence, Chigorin variation. In game 87 the engines castled in opposite directions, Stockfish gave a pawn to open the a file for its rook, Leela pushed a pawn to h6. Leela exchanged queens to avoid a queen side attack on its king, Leela's eval very slowly increased while Stockfish's eval decreased. After some shuffling Stockfish's eval started to increase, the engines reduced to a RRB vs RRN position.
The white rooks were very active, one on the a file and the other on the f file after it was opened. Stockfish concentrated its forces on the queen side, Leela exchanged a pair of rooks and managed to capture the h pawn, creating a dangerous advanced passer. Stockfish attacked the white king, Leela gave a rook for a knight and captured another pawn, creating a second passer on the queen side. The black rook could not defend against both passers, in the end Leela promoted both (one to a rook, why?) and the game ended in a tablebase win.
In game 88 Stockfish castled long and Leela kept its king in the center. Stockfish's eval increased very quickly, it pushed the g pawn forward to drive a knight away and then captured a pawn. Here the game started to go wild, Leela had a rook hanging but it moved a pawn on the queen side, Stockfish did not take the rook and let it escape in the next move. I assume Leela was threatening a queen side attack and Stockfish had no time to waste. Leela captured a pawn on the queen side, Stockfish refused to take back, again not wanting to open files there. Instead its queen moved forward and captured another pawn on the king side. Again the black rook was under attack, Leela countered with a threat to the white queen. On move 19 Stockfish re-countered with a threat to the rook, and then Leela didn't take the queen and its rook was still hanging. Crazy stuff !!
It's impossible for me to understand what the engines were doing, Stockfish had threats on the king side with 2 pawns advancing while Leela threatened an attack on the white king, it just needed a tempo to do it. The white queen moved to safety, Leela captured a knight with its rook which was still hanging. Stockfish didn't retake, instead it pushed the g pawn to the 7th rank. Leela left a knight hanging as well, it captured a pawn on the queen side to further expose the white king. Leela gave a bishop for the g7 passer, the black rook was still hanging but Stockfish preferred to capture a knight near its king. That rook was hanging for 10 moves and it survived. Most of the craziness was over, the engines exchanged queens and Stockfish gave a rook for a knight. On move 39 the end results were a BN vs R imbalance, it seemed such a small material advantage but evals were over 10.
Both engines had passers but the white passer on h6 was more dangerous. Stockfish used its pieces to drive the black king away, then it gave the passer but captured a rook for a knight. In the RB vs R ending Stockfish made sure it had a pawn left, the game ended in a tablebase win. There were two white wins in this game pair, Stockfish leads 22-8.
Games 89-90 started with a rare sideline of the closed Sicilian defence. In game 89 both engines castled long and queens were off early. Evals stayed high as Leela created a central passer, the engines exchanged pieces until only RRN vs RRN were left. After some shuffling Stockfish's eval suddenly dropped, it had a weak pawn structure but somehow it managed to hold everything together. Leela's eval came down as well, the engines shuffled for a while and then exchanged a pair of rooks. The game was adjudicated when enough pawns were exchanged.
In game 90 Stockfish castled long and Leela kept its king uncastled. Evals gradually increased, Leela tried to attack on the queen side and it opened the a file. Stockfish attacked through the center, in a long PV agreement (that Stockfish already saw from move 19) the engines exchanged most pieces. The game reached a RB vs RB position on move 30, with Stockfish a pawn up.
The engines traded pawns until there were only 2 white pawns (c+d) and one black (b). Stockfish improved very slowly, after 15 moves it managed to safely move its king in front of the pawns, both of them on the 5th rank. The black king was forced to the king side, nothing could stop the white pawns and Leela gave up, Stockfish queened and mated. Stockfish wins the game pair, it leads 23-8.
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