Sunday, February 24, 2019

Season 14 superfinal, games 91-100

Stockfish won the season 14 superfinal. The final score is 10-9 with 81 draws.
The last 10 games ended in a draw and weren't that exciting, except for the anticipation at the beginning of each game to see whether it would turn out to be decisive. In the end Stockfish held on to the small one point lead to win the match.

Superfinal summary
This superfinal match has been one of the best I've seen in TCEC, if not the best so far. After several seasons of Stockfish dominance this superfinal was really competitive and the result was very close until the very end. Leela's journey in this season was remarkable, it got better every time it was updated on its way up from division 3. I was surprised that it was so close to winning based on its performance in the premier division. Recall that it was very close to Houdini and Komodo, Stockfish had a much better score.

There were many decisive games at the start of the match, Stockfish led 6-3 after 22 games, including one game pair where Stockfish won from both sides. Leela closed the gap to 6-6 after 30 games, and after 19 straight draws Leela took the lead, after 60 games it was ahead 8-7. Leela continued to lead by 1-2 points but Stockfish kept close until it equalized to 9-9 after 80 games. Then Stockfish won a game to lead 10-9 and held on to this small lead until the end.

Stockfish may have won this superfinal, but it seems likely that Leela (NN based engines in general) may be the future of computer chess. There were many games where Leela played the opening much better than Stockfish, getting to positions where Stockfish realized it was worse or losing. Leela's closing skills are still lacking, it allowed Stockfish to escape many times. There was even one game where Leela failed to convert a 7-man tablebase win, despite having access to 6-man tablebases. Some of Leela's losses were a result of not looking far enough ahead and making a losing move, sometimes realizing it was losing immediately and sometimes many moves later. To summarize, it seems Leela is already better than Stockfish in some aspects of the game, and it needs to improve its skill in converting wins and calculating ahead. There are suggestions of a hybrid approach, who knows how much better engines can get.


Games 91-92 started with a 23 ply book sequence in the Frence Defense, Winawer variant, where both kings are still in the center and white has a king side passer. In game 91 Stockfish castled long and Leela kept its king in the center. Stockfish gave 3 pawns and moved pieces forward on the king side, Leela's eval climbed over 1.5. Stockfish then gave a rook for a bishop, its two knights attacked the king side and Leela had to be careful. The tension was resolved in a series of exchanges, Stockfish ended the game in a perpetual check. In game 92 Stockfish went a pawn up and pushed its passer to the 7th rank. Evals stayed below 1 and slowly came down. Leela blocked the pawn and slowly exchanged pieces, by move 47 the passer was gone and the game reached a rook ending. The game was adjudicated 20 moves later.

Games 93-94 started with black a pawn up and white with much better developement and a king that cannot castle. In game 93 Leela's eval started over 1. Stockfish gave back the pawn and created a passer on the queen side, then pushed it all the way to the 2nd rank. Leela controlled the center and the black king remained uncastled. Leela temporarily sacrificed a knight and opened the king side. Leela's eval jumped over 2 and then after a series of exchanges only RRN vs RRN remained on move 39. Leela tried to give a rook for a knight, but couldn't break Stockfish's defense. The game ended in a tablebase draw on move 122. In game 94 the evals stayed under 1. Stockfish traded NN for R and opened the king side, Leela gave a rook for a bishop that resulted in an unusual imbalance RR vs BBN. Evals dropped to 0 and the game was adjudicated by the draw rule on move 36, with perpetual check expected in the PV.

Games 95-96 were another King's Gambit variant, black started a pawn up. In game 95 Leela gave a second pawn and the queens were off early. Both kings moved and didn't castle, evals were negative but started to come down after move 20. Leela equalized the material, Stockfish still had a king side passer it pushed to the 3rd rank. Stockfish gave material to clear the path for its passer, then won the material back after the passer promoted. The game reached a B vs R ending and a tablebase draw. In game 96 there were many early exchanges and only RBN vs RNN were left on move 21. Leela's eval was negative over 1, Stockfish's eval dropped to 0 after the engines reduced to a BN vs R ending. The rest of the game was a long shuffle until Leela lowered its eval, and then a tablebase draw again.

Stockfish's eval stayed low in game 97, Leela's eval was under 1. The black king remained in the center, Leela gave a rook for a bishop but didn't get any initiative as a result. Stockfish gave the material back and the engines reduced to a queen ending on move 36. Stockfish ended the game in a perpetual check more than 50 moves later. In game 98 Leela pushed pawns on the queen side and had a space advantage. Only one pair of pawns was exchanged until move 20 and evals were close to 0. The engines started to exchange pieces and pawns gradually, on move 48 Leela gave a knight for pawns and the game reached a RBN vs RB position. Stockfish stopped the black passers on the 2nd rank and the game ended in a tablebase draw.

Games 99-100 started with a 26-ply book sequence in the Sicilian Najdorf opening. In game 99 Stockfish kept its king in the center, its eval was 0 after 2 moves and stayed there throughout the game. It opened the queen side and attacked with its queen, Leela's king was forced to run to the center. Leela exchanged queens so its king would be safe despite being exposed, on move 34 only RBN vs RBN remained. After exchanging rooks Leela went up two pawns, but the bishops were of opposite colors and  there wasn't enough material for a win. The game ended in a tablebase draw. Stockfish was almost sure of winning the match at this stage, one point ahead and a white bias in the last game. Leela castled short in game 100, then pushed pawns on the queen side towards the white king. Stockfish allowed a black pawn to get to b2 and hid its king behind it. Leela concentrated its major pieces on the queen side and the white king walked to the center. The engines reached a standoff, evals came down and the engines started shuffling. Thankfully, Leela reduced its eval close to 0 and the game ended quickly by the draw rule. This draw confirms Stockfish is the winner of the superfinal.


  1. Is true that Leela has disconnections and had to restart some games?

    1. Sometimes there are network failures that stop games. The GPU and CPU servers are not on the same machine and if the connection fails the game stops. This happened for example in game 66, and the game was replayed.