After 50 games Stockfish leads 15-9 with 26 draws. Stockfish won two game pairs and extended its lead to 6, the highest so far in the match. This is the same result as in the last season's superfinal at the half way point. Last season Leela had a significant comeback in the second half, will we see this again this season? There were two game pairs with two white wins, Stockfish's win in game 46 displayed another case where Leela evaluates completely won endgames as a draw - this time it was an 8-man RB vs RB position with white two pawns up.
Games 41-42 started with a rare line in the QGD, Stonewall variation. In game 41 there were almost no exchanges after the start and all pawns were on the board. Leela pushed pawns on the queen side and Stockfish blocked with its pawns. On move 23 there was on pawn exchange on the king side, Stockfish placed a rook and a queen on the half open h file but Leela protected its pawns there. The engines started to shuffle, the white king walked to the queen side and evals came down. On move 79 Leela gave a pawn, then all rooks were exchanged. The game reached a QB vs QB position and was adjudicated on move 99.
In game 42 the engines opened the b file and Stockfish moved a rook to the 7th rank. After some shuffling with low evals Stockfish exchanged a pair of rooks and its eval jumped over 1. The engines exchanged queens and the game reached a RBB vs RBN position. Leela's eval was still below 1, it felt safe.
Stockfish's eval went over 2 as it blocked the center, the white king walked to the queen side and the engines shuffled for a long time. Leela's eval also increased though it seemed nothing was happening. Stockfish placed a bishop on b5 and Leela did not capture it on multiple opportunities. The white king moved back to the center, finally on move 91 Stockfish moved the rook to the king side and captured two pawns.
Stockfish gave a rook for the black e pawn, then captured the a pawn, so it had 3 passers. It pushed the a pawn to the 7th rank, Leela managed to capture it with its knight but lost its bishop. Stockfish gave a pawn but secured the h8 square, Leela captured the h pawn and lost its knight. Stockfish queened the 3td passer and mated. Stockfish wins the game pair, it leads 12-7
Games 43-44 started with a 22-ply book in the Sicilian Richter-Rauzer variation. In game 43 the engines exchanged all knights, Stockfish kept its king in the center and its king side rook developed through the h file. The engines played out a long PV agreement and evals started to increase, despite a black doubled passer on the king side. The black king tried to find safety on the king side, Leela captured a pawn on the queen side and created connected passers. Stockfish captured a pawn on the king side and connected another passer there.
Stockfish exchanged a pair of rooks and moved its queen forward, Leela just pushed its pawns forward on the queen side, the c pawn became a third passer. After exchanging queens Stockfish pushed its passers on the king side and Leela stopped them. A series of exchanges reduced to a same color bishop ending, Leela queened twice and mated.
In game 44 only one pair of knights was exchanged. Evals gradually increased, the engines opened the h file and exchanged a pair of rooks. Leela castled long, then in a series of exchanges the engines reduced to a QBB vs QBN position on move 29.
The black king was exposed and threatened by the white pieces. After exchanging a bishop for a knight Stockfish saw the win, it captured a pawn and waited for the right moment to exchange queens. Stockfish was two pawns up in an opposite color bishop ending, the white king moved forward and Leela couldn't block all the white passers. Stockfish queened and the game ended in a tablebase win. There were two white wins in this game pair, Stockfish leads 13-8.
Games 45-46 started with a rare Queen's pawn, anti Torre line. In game 45 both queens moved forward on the queen side. Leela's eval started to increase early while Stockfish still thought it was safe. In a series of exchanges the queen side was opened, queens were off, Stockfish was a pawn up with a passer on c3. Leela pushed a passer to d6, Stockfish castled long and its eval increased as well. Leela also castled long, the game reached a RRB vs RRN position, Stockfish captured a second pawn while Leela connected a second passer in the center. Stockfish used its two rooks to block the white passers.
Stockfish's only strength was the queen side passers, the black king moved forward and supported their advance. Leela captured the c3 pawn and then cleared the king side and created a passer there. Stockfish managed to switch a blocking rook with a knight and capture the e pawn, but then Leela captured all the three queen side pawns. Stockfish couldn't prevent a queening, the game ended in a tablebase win.
In game 46 the engines opened the queen side and both castled short. Stockfish moved its queen forward and exchanged queens. Evals stayed below 1 though Stockfish captured a pawn, the game reached a RRB vs RRB position on move 39. Stockfish captured a second pawn but both engines were still unconvinced.
The engines traded a pair of pawns and exchanged a pair of rooks, leaving an 8-man position with only two white pawns on the king side. Evals stayed low for a while, perhaps because of the opposite color bishop ending that would be the result of exchanging the rooks. Starting from move 65 Stockfish's eval slowly increased, then jumped over 2 when it pushed a passer safely to h6. Leela's eval became even lower while Stockfish's eval was a clear win, the white king and g pawn slowly moved forward. On move 93 Stockfish's eval was over 90, Leela's eval only 0.32 !!
Leela's eval finally started to react, while Stockfish saw the win in its PV. On move 114 Stockfish pushed the g pawn and reset the 50-move counter, then it drove the black king forward out of the corner. Stockfish queened one of the pawns and the game ended in a tablebase win. There were two white wins in this game pair, Stockfish leads 14-9
Games 47-48 started with a line in the Dutch, Ilyin-Zhenevsky variation played in high level human games. In game 47 the engines exchanged pawns and knights in the center and evals came down. From move 22 the engines exchanged pieces until the game reached a QR vs QR position. Evals were low and the game was adjudicated early on move 37.
In game 48 the engines exchanged a pair of pawns and a pair of knights in the center, like the start of the reverse game. Then the engines opened the c file and Stockfish moved a rook to the 7th rank. Stockfish's eval slowly increased while Leela's eval remained low. Stockfish moved a second rook forward, in a series of exchanges the queens were off and Stockfish gave a rook for a bishop and two pawns. The black king was exposed and white had two connected passers on the king side, Leela's eval was still low.
Leela thought for 10 minutes and its eval jumped. In a series of exchanges the engines reduced to a rook ending with white a pawn up. Leela also had connected passers but they were slower, and Stockfish had an additional passer on the queen side. Leela tried but couldn't stop the white passers, Stockfish queened twice and mated. Stockfish wins the game pair, it leads 15-9
Games 49-50 started with a the Semi-Benoni variation of the Benoni defense, the center was blocked. In game 49 there were only a few exchanges after the start, Stockfish placed a bishop on h3 and exchanged the other. Leela exchanged a pair of knights and its eval increased to over 1.5. Stockfish's eval came down, it opened the f file and gave a rook for a knight. Stockfish captured a pawn on the king side and the exposed white king walked to the queen side. Leela's eval came down, Stockfish gave another rook for a bishop and threatened the white king. Leela reacted with a threat on the black king through the open g file. The engines reduced to a QR vs QN position and the game was adjudicated. In game 50 the engines exchanged pawns and minor pieces and opened the e file. Evals stayed under 1, after a while the engines exchanged a pair of rooks and evals came down. Stockfish captured a pawn and the game reached a QRN vs QRB position. The game was adjudicated after queens were exchanged.
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