Stockfish wins the season 18 superfinal. The final result is 23-16 with 61 draws. This was the expected result and Stockfish increased its lead to +7 despite Leela winning a game pair.
This was the 4th time Stockfish and Leela played in a TCEC superfinal with two wins each. Last season Leela won convincingly, and since that was only 3 months ago I was sure this season would be similar. I was really surprised when the match started with Stockfish winning 3 game pairs in the first 10 games. In the next 40 games the match was more balanced and Leela even reduced the lead to +2. However, Stockfish again won 3 game pairs in 10 games and extended the lead to +5, Leela never recovered from this. Many people had various opinions about why this season Stockfish won / Leela lost the match, fans were either gloating or shouting "scam". In my opinion this was a combination of the hardware, software, opening choices and pure luck. In other words, I have no idea, just enjoying the ride.
Last season I thought a draw rate of 71% was unusually low for a superfinal. This season it was only 61%. This was intentional, Jeroen stated that he preferred more decisive games and his opening choices were more biased than usual. Indeed, there were 11 game pairs with a biased 1-1 result of two white wins.
Looking back at this season, it ran very smoothly compared to last season. The hardware was ready, there were no format changes due to technical limitations. The lower 4 leagues ended very quickly, each was a 1-DRR event with 10 engines and relatively short time controls. The leagues were quite stable in that 7 of the 8 engines that promoted were immediately relegated back in the next league. The premier division started with a possible upset, Stoofvlees led the table after the first DRR one point ahead of Stockfish, Leela and AllieStein. Order was restored when Stockfish beat both AllieStein and Stoofvlees and took the lead. In the end Stoofvlees was only 4th, AllieStein lost a game to Komodo and only managed 3rd place, and we got the classic expected superfinal Stockfish - Leela.
I'm not sure when season 19 will start, there are various bonus events and the TCEC cup that will be played first. I need a break, but with the corona virus in the air no one is going anywhere.
Stay safe, everyone, and Go TCEC !!
Both engines castled long in game 91, the center was blocked and Leela had more room for its pieces. Leela opened a file on the king side and doubled its rooks there, then the engines shuffled for almost 50 moves before Leela moved a pawn. Most pieces were exchanged and the game reached a RB vs RB position on move 100. Stockfish's eval came down to 0, it reduced to a same color bishop ending. Leela played on, the game was adjudicated only on move 192.
The engines castled short in game 92, then pushed pawns on the queen side. A series of exchanges opened the queen side and left a QRR vs QRR position on move 22. Stockfish's eval was over 2 and increasing, it went a pawn up and it had a central passer.
Stockfish moved a rook to the king side and together with the queen threatened mate in the corner. Evals continued to increase as Leela defended its king and weak pawns. Leela decided to exchange queens and then a pair of rooks. Stocfish was confident the rook ending was a win though material was equal.
Leela couldn't protect both pawns on the 6th rank and Stockfish captured a6 and created a second passer. Leela was able to stop one but Stockfish promoted the other to a queen and won. Stockfish wins the game pair and the lead increases to +7.
All pieces and pawns were on the board until move 20 in game 93. The engines locked the queen side, Stockfish moved its queen forward on the king side. Evals slowly increased while the engines exchanged a few minors, a pair of pawns and the queens. Material was equal but black's pawn structure was worse.
The engines exchanged a pair of rooks, Stockfish tried to hold on to its weak e pawn and Leela exchanged it for its f pawn. Material was still equal but now Leela had a passer, even though it was still on e2. Stockfish's eval was close to 5, reflecting how dangerous it thought the passer was.
Leela exchanged the white knight that blocked the passer. The white king came forward and captured a pawn that the black pieces were too busy to protect. Leela forced the black king out of the way and created a clear path for its passer. The game ended with Leela giving a rook for a bishop to ensure promotion.
Game 94 was more open, there were a few minor piece exchanges after the start and Stockfish kept a bishop pair. The engines opened a file on the queen side, Stockfish let Leela control it while it planted a bishop on d6. Leela went a pawn up and the king side opened, Stockfish's eval increased as it saw a possible attack on the black king. Leela doubled rooks on the queen side, with a pawn on e3 it thought it had a strong enough attack on the white king. Stockfish thought otherwise, its eval jumped over 5.
Leela exchanged a pair of rooks and a pair of bishops, its remaining pieces surrounded the white king. Stockfish went after the black king, every tempo was crucial to the point where Stockfish chose to promote a pawn to a knight with check instead of a queen.
A few moves later the white knight forked the black queen with check, giving Stockfish the win. There were two white wins in this opening, Stockfish's lead is still +7. With 6 games to go Stockfish is officially the winner.
Games 95-96 started in the Russian game, with white sacrificing a knight for two pawns and forcing the black king to move. In game 95 Leela castled long and Stockfish's king completed a short castling by walking to the king side. Stockfish opened the queen side with its pawns, Leela opened a file on the king side. It seemed the black king was more exposed, yet Stockfish's (negative) eval slowly increased. Stockfish gave the piece back and captured a pawn, opening a file and creating a central passer. The engines exchanged a few pieces and Stockfish's eval started to jump. The game reached a QRN vs QRN position on move 47, both engines had advanced passers and material was equal but Stockfish was sure it was much better.
Leela had to protect its pinned knight, as well as move the king safely to remove the pin. Stockfish used the time to capture the white passer, and it covered all squares where Leela could attack the black king. Leela captured the black passer at the cost of losing its knight, Stockfish already saw the win.
The 7-man Q vs QN position was very easy for Stockfish, the game was adjudicated very quickly with the PVs showing how Stockfish can force a queen exchange and win with its knight and last pawn.
Stockfish castled short in game 96 and evals stayed low. Stockfish pushed pawns on the king side and its queen came forward on the queen side. After the king side opened Leela had to protect its king from the white heavy pieces, after exchanging queens Stockfish forced a 3-fold repetition draw. Stockfish wins the game pair and is lead increases to +8.
Games 97-98 started with a 22-ply book, a popular line in the King's Indian Defense, Bayonet attack variation. There were only a few exchanges after the start of game 97, Leela had more space on the queen side and both engines played behind their pawns. After some shuffling evals started to increase, Leela concentrated forces in the center where Stockfish had an isolated pawn. Stockfish decided to give a rook for a bishop and pawn.
Leela attacked the black e pawn and Stockfish defended with all its available pieces. The engines exchanged minor pieces and the game reached a QRR vs QRB on move 55, evals increasing all the time. Leela shuffled for 20 moves before it captured a pawn on the king side and created a passer.
Leela used its pawns to open the king side, Stockfish exchanged queens and Leela captured another pawn. Its two passers on the king side secured the win.
The engines locked the center in game 98, Stockfish pushed pawns on the queen side and opened it with pawn exchanges. Stockfish gave a pawn and tried to attack on the queen side, its eval was over 1 yet not increasing. After exchanging a few minor pieces Stockfish opened another file and regained the pawn, however Leela covered the entry points on the queen side and the engines started to shuffle. After 30 moves the engines exchanged a pair of rooks, then shuffled again. Leela pushed a pawn to the 7th rank, evals came down slowly as the engines exchanged pieces and reduced to an opposite color bishop ending on move 115. The game was adjudicated on move 148. Leela wins the game pair, Stockfish's lead is back to +7.
The engines opened the king side in game 99, Leela castled long and Stockfish did not castle at all. Leela exchanged queens and went up a pawn, then it cleared the black queen side pawns and created 3 queen side passers. Nevertheless Stockfish's eval came down to 0, it regained the pawn and its rooks controlled the back ranks. Leela gave a rook for a knight to keep its bishop pair, the game reached a BB s RB position. Both engines had advanced passers, the game was adjudicated before exchanges led to an opposite color bishop ending. In game 100 the kings' setup was similar, this time the engines opened the king side and most of the queen side pawns remained on the board. After exchanging queens the engines shuffled for a while and evals came down. The game reached a RBN vs RBB position, both engines pushed a passer forward and a series of exchanges led to a rook ending. Stockfish was two pawns up but Leela's single pawn was supported by the king. Leela captured a pawn and the game ended in a tablebase draw.