After 60 games Stockfish leads 9-6 with 45 draws. There were 6 decisive games in the last 10, two double white wins and two stockfish wins. A lead of +3 is still small but compared to the results so far it may be significant with 40 games left in the match.
In both games 51-52 the engines castled in opposite directions. In game 51 there were many early exchanges. Leela's eval was constant around 1 while Stockfish's eval increased steadily. Leela pushed pawns on the king side and one pawn reached h6. The game reached a RRB vs RRB position on move 22, material was equal yet Stockfish's eval was over 2.5.
The action was on the queen side and the black king walked slowly to get there. Stockfish was caught in a web of pins in the center, and Leela threatened to play c4 and open a file in the center for its rooks. Stockfish chose to give a rook for a bishop to release some of the pressure.
Leela slowly shifted its rooks to the queen side and targeted the b pawn.Stockfish tried to keep files closed and it allowed the white a pawn to advance and become a passer. Then the white king came forward and Leela created a second passer in the center, the game was adjudicated a few moves later.
In game 52 Stockfish's eval jumped over 2 on move 14. It prepared its pieces for an attack on the king side after exchanging a defending bishop. Leela saw an opportunity to fork two white pieces with a pawn, Stockfish ignored this and went ahead with the attack.
It was quite incredible to see how long the d4 pawn could take a white piece, Stockfish played on and ignored it and Leela had more urgent things to do defending its king. Stockfish pushed the f pawn and used it to expose the black king. Leela had to avoid taking another free bishop because of a mate threat along the h file. A temporary rook sacrifice opened another file on the king side, Stockfish got the rook back and continued the attack. On move 32 Leela finally took a bishop with the d4 pawn, both the pawn and the bishop were static for more than 10 moves.
The second white rook joined the attack and Leela was forced to give its queen for a rook to avoid mate.The engines reduced to a Q vs RN position, Stockfish started to capture pawns and the game was adjudicated. Two white wins in this opening, very different games. Stockfish continues to lead by one win.
Stockfish opened the center early in game 53. The engines started to exchange pieces and Stockfish's eval came down. On move 34 the game reached a queen ending. After a while Leela went a pawn up, but Stockfish threatened either mate or perpetual check and this prevented Leela from capturing more pawns. Leela lowered its eval very slowly, the game was adjudicated on move 126.
In game 54 there were less exchanges after the start and the center remained closed. Stockfish thought Leela blundered in move 18 and its eval jumped over 1.5. It pushed a pawn forward and used a pin to exchange a pair of pawns and to create a passer in the center. This was also a restriction on the movement and influence of the black DSB.
Leela tried to exchange queens and Stockfish refused twice. Stockfish focused on the queen side, after exchanging a pair of rooks it captured a pawn. Leela's king walked back to the center to help with blocking the passer, evals increased and were over 4 on move 38.
Leela moved its queen forward in a desperate counter, Stockfish gave a knight for another pawn on the queen side. The black king was caught in a mating net and the game was adjudicated before Stockfish won more material. Stockfish wins the game pair and increases its lead to +2.
Games 55-56 started with the King's Gambit Declined, Norwalde variation. In game 55 Stockfish was a pawn up while Leela was far ahead in developing its pieces. Leela's eval remained under 1 with a very slow increase, Stockfish's eval jumped over 2 after Leela gave a second pawn on the queen side. Leela's eval jumped a few moves later, Stockfish captured a third pawn while Leela prepared for an attack on the black king.
The immediate danger was the b1-h7 diagonal. Stockfish captured the b1 bishop with its rook, Stockfish exchanged knights on f6 before taking back. The second white knight came forward and the black king was still vulnerable. Leela gave a rook for a bishop, when it seemed the attack was over Leela used a queen sacrifice and a knight fork to reduce to a RBN vs RB position.
Stockfish was 4 pawns up but all its pawns were isolated. Leela used its extra piece to pick the black pawns up one by one. After 30 moves Stockfish was down to its last pawn and the game was adjudicated.
In game 56 Stockfish regained the pawn right away, evals remained almost constant for a long time. Stockfish had a two bishops aimed at the black king, its LSB was on a strong central square. However Leela's defense looked solid and Stockfish didn't seem to have a plan. On move 24 Leela exchanged a pair of pawns on the queen side and its queen moved forward. Stockfish exchanged a pair of knights, its eval started to increase and was approaching 2.
Stockfish doubled rooks on the f file and the plan seemed to be attacking the f7 pawn. Stockfish could potentially attack with 4 pieces, Leela had 4 defenders without counting the king. Stockfish's jumped when it opened the h file with its pawns, Leela still thought it was OK.
Leela expected a quick rook exchange on the h file, Stockfish had other ideas and Leela's eval immediately reacted. WIth one black rook in the corner Stockfish saw the opportunity, it exchanged the defending knight and captured the f7 pawn. The black king was caught between the open f and h files and Stockfish saw the mate coming. The game was adjudicated after Stockfish gave its queen for a rook, the PV showed how it could regain the material and win. Two white wins in the opening, Stockfish still leads by +2.
Leela captured a pawn and queens were off early in game 57. Stockfish placed a rook on the 2nd rank and then regained the pawn using a pin on the long diagonal. Stockfish captured another pawn and Leela placed a rook on the 7th file. Evals came down and in a series of exchanges the engines reduced to a RBN vs RR position on move 34. Both kings were exposed to checks by the rooks and the game was adjudicated by the draw rule. In game 58 Leela opened the queen side and after a series of exchanges the game reached a QRB vs QRB position on move 21. After a few pawn moves the engines started to shuffle. Stockfish controlled the open a file but Leela covered the back ranks. Leela's eval kept the game going, Stockfish captured a pawn and avoided the 50-move rule. The engines exchanged more pieces and pawns and the game was adjudicated in a drawn rook ending.
Games 59-60 started with the Alekhine defense modern variation, in a position from a Spassky-Fischer game. After a few early exchanges in game 59 the engines started to play behind their pawn lines. On move 26 Stockfish opened the c file, the engines exchanged all rooks and the game reached a QBB vs QNN position on move 34. Stockfish used its knights to block the open files and the engines started to shuffle. Leela wouldn't lower its eval, near the 50-move rule it reduced to a B vs N ending. Both engines had passers that raced forward, Stockfish was first and Leela lost its bishop for a passer. The black knight was in time to stop the white passers and the game reached a tablebase draw.
In game 60 there was one minor piece exchange after the start, all pawns remained on the board. The engines locked the center and queen side, with a small opening on the king side. Stockfish had more space and its eval was over 1.5, the engines started to shuffle on move 28. On move 73 Stockfish exchanged a pair of pawns on the queen side, its eval came down a llittle and shuffling resumed. On move 101 Stockfish moved a pawn, both engines were playing on increments. Stockfish's eval continued to drift down, it went under 1 for a while and then started to increase after move 140. Leela grabbed a free pawn on the queen side and suddenly Stockfish thought it had something.
The f6 square was vulnerable, Leela had to move its knight to let the king out of the corner. Stockfish exchanged the knight for a bishop and doubled rooks on the g file. Then it forced the g file open with a queen sacrifice and captured h7. The black king had to run away to avoid a back rank mate by the white rooks, and Leela could not stop the white h pawn queening.
Leela captured a knight, but with so much firepower on the back rank Stockfish regained the material quickly. A series of exchanges reduced to a bishop vs pawns ending and a win for white. An unexpected end to a very long game. Stockfish wins the game pair, its lead is +3.
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