Friday, February 8, 2019

Season 14 superfinal, games 15-20

After 20 games Stockfish leads 4-3 with 13 draws.
There have been 7 straight decisive game pairs. This is quite unexpected in a superfinal, the current draw rate is 65% which is quite low. 

In game 15 Leela castled long and Stockfish pushed its queen side pawns forward. Leela was better on the king side but it was too busy defending its king. A series of exchanges removed Stockfish's threats and the game ended quickly in a tablebase draw.
Game 16 started with a similar setup. Stockfish castled long and Leela pushed its queen side pawns. This time Leela was slower with its queen side attack, instead it broke up the white king side pawn structure, moving a rook so it couldn't castle. Leela captured a pawn, allowing Stockfish to take over the open h file with the black king in the center. Stockfish's eval jumped over 2 as it found a great outpost for its LS bishop, attacking from the queen side.

WIth the king trapped in the middle Leela didn't stand a chance. In a QRB vs QRN position Stockfish opened the center with its pawns and had enough strength to force either mate or significant material loss. Stockfish is back in the lead after this game pair.

In games 17-18 white started a pawn up in a Budapest Defense opening. Leela started game 17 with an eval around 1, then it gave back the pawn and its eval climbed over 1.5. On move 20 Stockfish captured a knight and expected it to be retaken by the white queen. Leela surprised with a retake with the pawn, its eval jumped over 3.

Stockfish traded its queen for two rooks leading to an unusual QBB vs RRNN position. Stockfish tried to build a fortress, it put its queen side pawns on dark squares based on c7, and tried to block the light squares with a protected knight on e4. It couldn't prevent Leela's LS bishop from getting to the queen side, and a mate threat caused the fortress to crumble.

Leela pushed its king side pawns and captured the c7 pawn, the game was adjudicated after Stocfish lost one of the knights.
In game 18 Leela exchanged queens early. Stockfish kept the pawn advantage, its evals stayed below 1. The game reached a RRB vs RRB position on move 22, evals came slowly down as the engines traded pawns. When only one white pawn was left Leela's eval became negative. It captured a rook for a bishop, the position was a 7-man draw that went on for 25 more moves. A win for Leela in the game pair and the score is equal again.

Leela started game 19 with an eval over 1. After a series of exchanges only QRN vs QRB remained on move 24, Stockfish's eval was 0 after exchanging queens. Leela insisted that the game would continue, it lowered its eval only 100 moves later in a drawn N vs B ending.
In game 20 evals stayed mostly below 1. A long series of exchanges that started on move 18 opened the board up, and led to a R for B imbalance. Leela was up a pawn and had an advanced pawn-bishop pair on the queen side.

Leela pushed the c passer forward and moved its pieces to support the queen side. Its bishop and two pawns looked very dangerous, even more when it captured the a2 pawn. Leela's eval was close to 0, it was sure that its advanced passers compensated for Stockfish's small material advantage. Stockfish surprised with a knight sacrifice, its eval jumping to 2.5.

This exposed the black king. Leela understood the danger only 3 moves later, too late. The white QRR attacked the black king, Leela did not have enough defenders and it started to lose material. Stockfish gave material back to remove the black queen side passers, the game reduced to a R vs B ending and a win for Stockfish. After this game pair win Stockfish is back in front.

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