After 50 games Stockfish leads 20-11 with 19 draws. Leela won (only) its second game pair of the match, but then it lost a game on time for the second time and Stockfish won a game pair from both sides - something we haven't seen in a superfinal for a long time. The other 3 game pairs were drawn and Stockfish extends its lead to +9 at the halfway point. At this rate the final score gap may be close to record high for a superfinal.
Games 41-42 started with a sideline of the Nimzo-Indian defense, St. Petersburg variation. In game 41 there were no exchanges after the start, the engines formed pawn lines and moved pieces behind them. The center and queen side were blocked, Stockfish had a bishop in front of the pawns. On move 29 there was a pawn exchange on the king side, after move 39 there were a few minor piece exchanges. Leela's eval was close to 2 at some point but then started to drift down as the engines shuffled. On move 82 there was another minor piece exchange, Stockfish moved its king to the queen side and Leela moved its king to the center. After move 112 evals started to increase, the black forward bishop was trapped (though safe) and Leela managed to exchange queens and capture a pawn, creating a passer.
The black bishop was out of the game, Leela moved its rooks to the king side and its bishop forward, then pushed the g pawn. Stockfish exchanged pawns and captured the passer, but after a pair of rooks was exchanged Leela moved its rook to the 7th rank, attacking the black pawns. Leela captured two pawns and Stockfish couldn't prevent a queening. Stockfish delayed with checks but was eventually mated.
In game 42 the engines blocked the center and queen side, similar to the reverse game. There were no pawn exchanges and Leela kept its bishops behind the pawns, on move 30 the engines exchanged a pair of bishops. The engines blocked the king side as well and started shuffling. On move 62 there was a pawn exchange, Stockfish's eval increase for a while and came back down when the shuffle continued. Stockfish had one pawn move left, the game ended in a 50 move draw on move 150. Leela wins the game pair, Stockfish leads 16-9.
Games 43-44 started with a rare sideline of the English, Anglo-Indian defense, the black queen moved forward in the center. In game 43 Leela pushed pawns in the center and moved its queen forward on the queen side. After Stockfish castled Leela pushed a pawn to h6, Stockfish captured a pawn on the queen side and created a passer for both engines. Stockfish pushed its passer, Leela captured a pawn and moved its queen forward. At first Stockfish avoided exchanging queens, but after Leela captured the black passer the queens were exchanged. The engines reduced to a RRN vs RRN position, Stockfish regained the pawn and the engines started to shuffle. Stockfish's eval was 0, Leela's eval slowly drifted down. On move 85 Leela pushed the passer and reset the 50-move counter, but then it failed to move on time and lost.
In game 44 Stockfish thought Leela castled too soon, both evals jumped as Stockfish exchanged pawns and opened the h file. The white king stayed in the center and Stockfish doubled queen and rook on the h file. Leela tried to threaten the white king, in a series of exchanges the engines reduced to a QR vs QB position with black a pawn up.
Stockfish moved its pieces to the center and its king to the king side. The rook moved to the back rank and pinned the black bishop. Leela tried to delay with checks, it avoided exchanging queens. Eventually Stockfish captured the bishop and mate followed. Stockfish wins this game pair from both sides, it leads 18-9.
Games 45-46 started with a rare sideline in the Scandinavian defense. In game 45 there were no exchanges after the start, Stockfish was late developing its queen side. Leela pushed a pawn on the king side, after exchanging a pair of knights the engines opened the g file. In a long PV agreement the center pawns were cleared, most pieces were exchanged and the game reached a RB vs BN position with black two pawns up.
For a while it seemed Leela was not sure how to proceed and evals remained stable. When Leela moved the rook to the back rank Stockfish's eval started to increase. Leela managed to trap the black king on the h file and its eval also increased. Eventually the rook moved to the h file, the black knight and king moved away and Leela captured the h pawn on move 71.
Stockfish tried to counter Leela's passer by pushing its own passer to the 2nd rank. Leela blocked with its king and threatened to take the a7 pawn, even by sacrificing its rook, since its a pawn would be unstoppable. Stockfish couldn't take the passer, the black king moved away from the king side and Leela slowly captured more pawns. Stockfish lost more material, Leela queened a passer and mated.
In game 46 Leela developed its queen side pieces quickly, the engines exchanged minor pieces and a pair of pawns in the center and opened the d file. Evals increased steadily, Stockfish gave a pawn on the king side while Leela moved a rook forward on the queen side. Stockfish captured pawns on the queen side and created connected passers.
Leela moved its queen back to stop the white passers, Stockfish exchanged knights and moved its queen forward through the center. Leela captured one passer but now its king was in danger, it exchanged pieces and reduced to a rook ending with white a pawn up.
Stockfish had two passers, while Leela defended the white king captured the remaining black pawns. Stockfish then queened twice and mated. There were two wins in this game pair, Stockfish leads 19-10.
Games 47-48 started with a rare sideline of the Sicilian Najdorf, Zagreb variation. In game 47 the engines exchanged minor pieces and Stockfish moved its queen forward. Leela captured a pawn, opened the a file and exchanged a pair of rooks. Stockfish castled late and Leela kept its king in the center. Leela captured another pawn and created connected passers on the queen side. The game reached a QRB vs QRB position, Stockfish's eval dropped despite being two pawns down. The engines traded pawns, Stockfish blocked the white passers and Leela didn't find a way to improve. After exchanging queens Leela's eval dropped and the game was adjudicated. In game 48 the black queen stayed back, Stockfish pushed pawns on the queen side, opened files and created a passer. The black king moved to the king side without castling, Leela gave a rook for a knight and pawn and the game reached a QRR vs QRB position. Leela had passers in the center, Stockfish abandoned its passer and captured the two black passers. Leela's eval dropped as queens and more pawns were exchanged, Leela found a fortress, from move 51 it repeated rook moves while Stockfish shuffled. The game was adjudicated on move 99.
Games 49-50 started with a sideline in the Pirc defense. In game 49 the engines exchanged a pair of knights in the center, Leela moved a bishop to c6 and evals increased. Leela captured a pawn on the queen side and Stockfish gave a rook for the forward bishop and a pawn.
Leela opened the a file, doubled rooks there and moved a rook forward. Stockfish tried to keep the center and king side closed and to defend the open queen side. There was a pawn exchange on the king side, and Leela pushed a pawn forward on the queen side and created a passer. Then Leela captured another pawn in the center.
Leela captured pawns and opened files on the king side, threatening the black king. Stockfish lost more and more material and was mated.
In game 50 the engines exchanged minor pieces, then exchanged pawns in the center and Leela captured a pawn. Leela tried to hold on to its extra pawn and it didn't develop its queen side pieces. Stockfish's eval increased while Leela's eval decreased until it realized it was in trouble after a 17 minute think on move 20.
Leela moved its knight while Stockfish captured the e pawn and defended its passer, offering its bishop for several moves. Leela gave a rook for a knight in the center, Stockfish pushed the passer and Leela captured the bishop. Stockfish moved a rook to the 7th rank, then gave a pawn and opened the g file. Stockfish pushed the passer to the 7th rank and threatened the black king, in a series of exchanges Leela captured the passer and the game reached a Q vs RB position.
The engines traded pawns until there was only one white pawn and two black. Stockfish used checks and fork threats to push its pawn to the 7th rank, Leela gave the bishop to capture the passer. Stockfish converted the 6-man ending in 30 more moves. There were two wins in this game pair, Stockfish leads 20-11.
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