After 70 games Stockfish leads 22-12 with 36 draws. Stockfish won two game pairs and extended its lead to +10, the biggest lead so far. There was one game pair with two white wins, Leela was not able to win a game pair. In games 64 and 66 Stockfish won a very long endgame that seemed to be a draw.
Games 61-62 started with the Zukertort opening, Nimzo-Larsen variation, with an advantage for black. In game 61 the engines blocked the center and exchanged a pair of bishops. Leela pushed pawns on the queen side, (negative) evals came down. The engines opened the queen side, the engines exchanged more pieces and pawns and Stockfish captured a pawn. Both engines used active knights to trade queens and a pair of rooks, leading to a RNN vs RBN position. After clearing the queen side pawns and exchanging rooks the game was adjudicated. In game 62 the engines exchanged a pair of pawns on the queen side and then exchanged most minor pieces. Leela went up a pawn, Stockfish castled long and (negative) evals came down. After a series of exchanges on the d file the game reached a RN vs RN position. The engines cleared the queen side pawns and then started to shuffle. Leela wouldn't lower its eval for a long time, the game was adjudicated on move 75.
Games 63-64 started with a 20-ply sideline of the Sicilian, Richter-Rauzer variation. White castled long while the black bishops were undeveloped. In game 63 Stockfish castled long, Leela captured a pawn and opened the f file. Leela moved a rook to the 7th rank, after a while the engines reduced to a RB vs RB position with white a pawn up. The king side was cleared, Leela had a passer in the center. Stockfish stopped the passer on the 6th rank and the engines started to shuffle. Leela wouldn't lower its eval, the game was adjudicated on move 115 approaching a 50-move draw.
In game 64 Leela castled long as well, Stockfish kept the king side closed and exchanged pawns in the center. Stockfish went up a pawn, both engines created passers in the center. Stockfish's eval slowly increased, Leela moved its queen forward and its eval dropped for a few moves. Leela pushed its passer to the 3rd rank, Stockifsh captured a second pawn and created a passer on the king side.
The black queen moved in front of the rook while defending the d3 pawn, Stockfish used this to push its central passer to d7 safely. Combining mate threats and attacks on pieces Stockfish managed to push its h passer slowly forward. Then in a series of exchanges Leela captured both white passers and gave a rook for a bishop. On move 55 the game reached a RR vs RB position.
Leela still had an advanced passer, after exchanging a pair of rooks the passer reached the 2nd rank but the bishop no longer controlled the promotion square. Stockfish saw the win, it created an unstoppable passer on the queen side. After queening the game ended in a tablebase win. Stockfish wins the game pair, it leads 20-11.
Games 65-66 started with a sideline of the Owen's defense. In game 65 Leela's eval spiked close to 2 early. The engines opened the d file and then Leela thought for 10 minutes and its eval came back down. After a few pawn moves the engines started to shuffle and Stockfish's eval was close to 0. On move 62 the engines started to exchange pieces and pawns, Stockfish gave a bishop for 3 pawns and the game reached a QB vs Q position. After exchanging queens the game was adjudicated.
In game 66 there were many early exchanges and long PV agreements. The black king moved without castling and blocked the king side rook. Once the king walked to h7 the rook was freed, by then Stockfish managed to create an advanced passer on the queen side. The engines exchanged all rooks and the game reached a BN vs BB position on move 36.
Stockfish blocked the black passer and pushed its own to the 7th rank, Leela's DS bishop couldn't attack the passer safely. For a long time the engines shuffled, on move 77 they exchanged a pair of pawns on the king side. Evals stayed low until suddenly Stockfish's eval jumped over 2 on move 86. Nothing seemed to be different, but Leela's eval started to increase slowly as well. The white king moved closer to the passer, slowly Stockfish managed to move its pieces so that it could force a bishop exchange on move 103 (the d8 bishop can escape to e7 but then Bc5+ exchanges anyway).
Stockfish already saw the win. Of the next 19 moves after exchanging bishops the knight moved 15 times, Stockfish captured two pawns and finally managed to queen the passer with the knight blocking the possibility of taking the queen. A few moves later Stockfish mated. Stockfish wins the game pair, it leads 21-11.
Games 67-68 started with a rare line in the Philidor defense, Boden variation. In game 67 the engines castled in opposite directions, Stockfish pushed pawns on the queen side. A black pawn reached a3, Leela blocked the queen side and its eval started to increase. In a long PV agreement Stockfish gave a rook and captured a bishop using a mate threat. Leela gave pawns and opened the king side, after exchanging queens the game reached a RR vs RN position with black two pawns up.
Stockfish's eval slowly increased, the white rooks were active as defenders and attackers. Leela managed to capture three pawns and created a passer on the queen side. Stockfish had a passer on the king side but it wasn't strong enough. Leela connected a second passer after a pawn exchange, Stockfish could not prevent a queening and mate.
In game 68 Stockfish castled long, Leela gave a rook for a bishop to open the b file before castling short. Evals stayed below 1 for a long time, in a series of exchanges the engines reduced to a QRR vs QRB position. Leela captured a pawn and all the remaining white pawns were isolated. The engines shuffled for a while and on move 40 they exchanged queens. On move 47 Stockfish started to increase unexpectedly, the engines cleared the king side pawns.
For a long time nothing seemed to happen, Stockfish repeated a lot and Leela mostly waited for Stockfish to do something. Leela's eval didn't change until move 80. Stockfish attacked the black bishop with two rooks, Leela defended with king and rook and was very close to zugzwang.
The engines blitzed, evals increased quickly and Leela's defense collapsed. The engines traded pawns until there was only one left for each side. Stockfish saw the win in an 8-man position, it offered the pawn but Leela avoided exchanges because a 7-man position was a loss. Eventually Stockfish exchanged rooks and the game was over. There were two white wins in this game pair, Stockfish leads 22-12.
Games 69-70 started with a 20-ply line in the Dutch Stonewall variation, all pieces and pawns were still on the board. In game 69 Stockfish pushed pawns on the king side and exchanged minor pieces. Leela tried to avoid a pawn blockade, the engines exchanged more minor pieces in the center and all knights were gone. Leela opened the b file and evals came down, the engines exchanged a pair of rooks. After some shuffling the engines exchanged queens, the game was adjudicated in a RB vs RB position. In game 70 the engines exchanged a pair of pawns and most minor pieces on the queen side. Evals came down and the king side was blocked. The game reached a QRR vs QRR position and the engines traded pawns. On move 53 the queens were exchanged, evals were low and the game was soon adjudicated.
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