After 20 games Stockfish leads 6-3 with 11 draws. Leela won its first game pair, winning as white and then holding a fortress in a position Stockfish was confident it could win. Stockfish responded with two game pair wins, extending its lead to 3.
Games 11-12 started with a 16-ply book, a sideline in the KID Saemich variation. In game 11 Leela pushed the g pawn forward and didn't castle its king. Stockfish opened the king side and its eval dropped to 0 while Leela moved its king to the corner. The engines waited for the draw rule from move 23, the game was adjudicated on move 45 after enough pieces and pawns were exchanged. In game 12 Stockfish exchanged pawns on the king side and castled short anyway. For a while Stockfish's eval increased but then it dropped though it followed its PV. The engines exchanged many pieces and Stockfish created a central passer while Leela had a passer on the queen side. Leela stopped the white passer on the 7th rank, the exchanges continued and evals came down. Both passers were captured, the game reached a RN vs RN position with Stockfish a pawn up, only enough for a draw.
In game 13 after a few early exchanges Leela had a pawn majority on the queen side. For a while Stockfish's eval came down a little, Leela's move 24 was a surprise and Stockfish thought for 18 minutes with an eval jump. Leela captured a pawn and created a doubled passer on the queen side, the game reached a RRB vs RRB position.
Stockfish was busy blocking the passer on the queen side, the white king moved forward on the king side and Leela created a passer there.
Leela abandoned the pawn on a6, but the h passer was unstoppable and Stockfish lost material to capture it. The game reached a RB vs R ending, Leela made sure it had a pawn left to guarantee a win.
In game 14 there were several early exchanges that opened the board. Leela captured a pawn on the queen side, Stockfish's eval increased as it opened the king side. Leela thought for 14 minutes and its eval also increased, then it moved without thinking for 6 straight moves while Stockfish regained the pawn and exposed the black king. Stockfish's attack resulted in a Q vs RB ending, Stockfish's eval was over 4 while Leela's eval decreased. Stockfish managed to capture the bishop but Leela created a fortress and just waited. There was nothing Stockfish could do, its eval came down very slowly and the game was adjudicated on move 229. Leela wins the game pair, Stockfish leads 4-3.
In game 15 Leela pushed a pawn to h6 and trapped a black bishop in the corner. Queens were off early, Stockfish managed to get its bishop out of the corner and to exchange it. The game reached a RRB vs RRN position, Stockfish captured the h6 pawn and evals came down. There were too many pawns for the draw rule, the game ended only on move 81 in a repetition.
In game 16 Stockfish exchanged the h pawn, then in a PV agreement Stockfish captured a rook for a bishop and pawn. Stockfish gave a pawn to open the d file, then moved its queen to the back rank and trapped a black bishop and rook on the queen side. Leela captured another pawn, it threatened a white knight but couldn't take since its king was in danger. Stockfish's move 23 with the knight was a surprise with an eval jump over 4.
Leela's queen was under threat and it realized it's best option was to exchange the knight for the DS bishop. Stockfish traded its bishop for a knight, with the center open Leela had to develop its queen side pieces. The game soon reached a RR vs RB position.
Stockfish had one last pawn, it captured black pawns until there was only one left as well. The 8-man position was not trivial, Leela delayed as much as possible but couldn't hold. Stockfish pushed its pawn slowly forward, eventually it used its two rooks to mate on move 80. Stockfish wins the game pair, it leads 5-3.
Games 17-18 started with a 17-ply book, a sideline of the KID four pawns attack with a significant black bias. In game 17 Leela tried to find safety for its king, it castled short but the king side pawns were far ahead. Stockfish exchanged knight for bishop and used Leela's weakness on light squares to threaten along the long diagonal. On move 21 Stockfish offered a rook to open the diagonal.
Leela didn't take the rook, Stockfish doubled rooks on the open f file and moved its queen forward. Leela exchanged pieces to save its king, the game reached a BNN vs BBN position with Stockfish a pawn up.
The advantage was small but sufficient for Stockfish. After a few minor piece exchanges the engines reduced to a same color bishop ending. While Leela blocked a black passer Stockfish captured a pawn and created a second passer. Leela couldn't prevent a queening, game over.
In game 18 Stockfish kept its king in the center and opened the h file. In a long PV agreement Stockfish doubled rook and queen on the h file and threatened the black king, and the engines exchanged LS bishops. On move 20 Leela thought for 14 minutes and decided to diverge from the PV, Stockfish's eval dropped immediately. In a new PV agreement Stockfish castled long and the engines reduced to a QRR vs QRR position. Leela was a pawn up but evals were close to 0 and the game was adjudicated early. Stockfish wins the game pair, it leads 6-3.
Games 19-20 started with a KGA sideline and a black bias. In game 19 Stockfish exposed the white king which moved without castling. In a long PV agreement Stockfish castled long and moved its queen back, it didn't attack the white king that had no pawn support. The engines opened the g file, still Leela kept its king safe and (negative) evals came down. The engines exchanges pieces until only RN vs RN remained, Stockfish was a pawn up but evals were low and the game was adjudicated. Game 20 repeated the reverse game until move 19. The engines continued to exchange pieces in a PV agreement until only RRN vs RRN remained. The (negative) evals came down and the engines further reduced to a knight ending with Leela a pawn up. Evals were not low enough for the draw rule, the game was adjudicated on move 111.
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