After 30 games Stockfish leads 12-5 with 13 draws. Leela won its first game pair of the match, but then lost 3 of the next 4 pairs. Stockfish increased its lead to +7 despite the loss. Leela lost a game on time, very unexpected.
Games 21-22 started with an 18-ply sideline of the KID orthodox variation. In game 21 the engines exchanged a pair of pawns in the center and pushed pawns on the queen side, then they opened the b file. Leela captured a pawn and created a passer, the engines exchanged a pair of rooks and evals increased. In a long PV agreement Leela pushed the passer forward and exchanged minor pieces, Stockfish created a passer in the center.
Stockfish pushed pawns on the king side, Leela avoided opening files there. Leela moved pieces forward, the black king was threatened. Leela gave a rook for a knight and a pawn, creating two more passers.
Stockfish gave the passer, it lost more and more material until its king was exposed, mate followed.
In game 22 the engines opened the c file and kept the center closed, then mostly shuffled behind their pawn lines. By move 36 the pawn lines blocked the whole board except the open c file. The white king walked to the queen side and the shuffle continued for close to 50 moves. On move 80 evals suddenly jumped, Stockfish sacrificed a knight and created connected passers on the queen side. Leela also created passers there, a series of exchanges reduced to a QBB vs QBN position and evals came back down. The engines shuffled until exchanging queens, then the game was adjudicated. Leela wins the game pair, Stockfish leads 8-4.
Games 23-24 started with a 20-ply sideline of the Pirc defense. In game 23 Stockfish pushed pawns on the king side, then a long series of exchanges cleared the queen side pawns and Leela was a pawn up. Stockfish blocked the king side, the game reached a QRN vs QRB position and evals came down as the engines shuffled. The engines exchanged rooks on move 49, exchanged a few pawns after move 73 and the game was finally adjudicated on move 130.
In game 24 Leela exchanged a pair of pawns on the queen side, Stockfish gave a rook for a bishop and its eval increased. Leela was weak on the dark squares, it traded a knight for the white DS bishop, then Stockfish created a passer and captured a pawn. Stockfish thought Leela's move 23 was a mistake and its eval jumped, Leela agreed after a 20 minute think. Leela gave back the material and captured the white passer, Stockfish cleared the black pawns on the queen side and reduced to a queen ending with a pawn up.
Stockfish used checks to push the passer forward, Leela captured it on the 7th rank but lost a pawn on the king side. Stockfish saw the win in its PV, it captured another pawn and reduced to a 6-man tablebase win. Stockfish wins the game pair, it leads 9-4.
Games 25-26 started with a sideline in the English 4 knights variation. In game 25 the engines pushed pawns without exchanges, there were a few minor piece exchanges. Leela moved a bishop forward, the first pawn exchange on move 29 opened the a file and Leela moved a rook forward. Stockfish exchanged the forward bishop, a knight exchange blocked the center and reduced to a QRR vs QRR position. Evals came down, the engines exchanged a pair of rooks and Stockfish moved its pieces to the king side. Leela tried to open the king side, when it captured a pawn Stockfish moved a rook forward and gave checks. Stockfish gave the rook and Leela avoided a stalemate, giving time for the black queen to force perpetual check. In game 26 Stockfish exchanged minor pieces and castled long. The engines opened the d file, Leela moved its major pieces to the queen side and Stockfish exchanged a pair of rooks. Evals drifted down as the engines mostly shuffled, Stockfish captured a pawn and opened the a file. On move 69 the remaining rooks were exchanged, then on move 81 Leela failed to move in time and lost with evals close to 0. Stockfish wins the game pair, it leads 10-4.
Games 27-28 started with an 18-ply rare sideline in the Sicilian Najdorf variation, white castled long and the black king was still in the center. In game 27 Stockfish grabbed an early pawn on the king side, evals increased steadily from the start. The engines exchanged minor pieces on the king side and Stockfish created a passer. On move 28 Stockfish finally castled its king, despite having weak pawn support.
Leela captured the d6 pawn and moved a knight forward to f6, Stockfish gave a rook for the knight. Leela cleared the black queen side pawns and Stockfish cleared the white king side pawns so both engines had 3 passers. Each engine lost one passer and queens were exchanged, resulting in a RRN vs RBN position.
Leela pushed the passers forward and Stockfish defended with its rook and knight. Leela drove the black knight away, Stockfish gave material and tried a desperate passer run. Leela lost a rook for the passer, then queened and mated.
In game 28 the engines repeated the reverse game for 11 plys and Leela was up a pawn. Leela then decided to castle long, evals again increased steadily. Stockfish had a space advantage, for a few moves it could take a knight but refused so as to avoid a trapped bishop. When the black knight moved Stockfish exchanged bishops. In a long PV agreement Stockfish traded a rook for two minor pieces and created a passer on the king side. Leela had connected passers supported by rooks.
Stockfish blocked the black passers and Leela managed to protect them but couldn't push them forward. The white passer became a threat and Leela moved rooks to block it. Stockfish then shifted major pieces to the open g file. Leela captured a pawn on the queen side while Stockfish moved a rook to the back rank and exchanged a pair of rooks. The game reached a QNN vs QR position, Stockfish saw the win in its PV.
Stockfish gave a pawn and started to chase the black king with just the queen and one knight. The black pieces couldn't help, Stockfish captured the black queen, queened a passer and mated. There were two white wins in this game pair, Stockfish leads 11-5.
Games 29-30 started with a rare sideline of the French defense, the c file was open. In game 29 there were no exchanges after the start, on move 20 a pawn exchange opened the f file. The engines blocked the center, in a series of exchanges all rooks were gone and then the engines reduced to a BN vs BN position. Stockfish's eval was close to 0 but Leela played on, the engines blocked the queen side and Leela's eval slowly decreased. The game was adjudicated on move 113.
In game 30 there were no exchanges after the start, Stockfish's eval started to increase and on move 19 there was a series of exchanges in the center. The engines exchanged a pair of rooks and Leela's eval also started to increase, Stockfish captured a pawn and opened the d file. After exchanging queens the game reached a RB vs RN position.
The black king moved forward, Leela captured a pawn on the queen side and Stockfish moved the rook forward. The black king moved back and was trapped on the back rank, Stockfish exchanged the minor pieces and reduced to a rook ending two pawns up. The engines exchanged a pair of pawns, Stockfish won the 6-man position after 40 more moves. Stockfish wins the game pair, it leads 12-5.
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