Season 20 premier division, after RR2

Standings after RR2

Stockfish leads with a +6 score, including double wins against ScorpioNN and rofChade. Leela is second with a +4 score and no game pair losses. KomodoDragon, Stoofvlees and AllieStein follow, all with positive scores.

The 3 engines at the bottom have negative scores. They are ranked according to their head to head performance, ScorpioNN beat Ethereal in their game pair, and Ethereal beat rofChade.

Cato's choice of openings seems to be more biased than usual for the premier division. The draw rate is under 50%, there are very few black wins and an unusually high number of double white wins. The top 5 engines are clearly better than the bottom 3 engines. Of the 15 game pairs between them 13 have been decisive in favor of the top 5 engines.

KomodoDragon is a definite improvement compared to the Komodo versions that played in the last few seasons. In season 19 Komodo struggled to avoid relegation, this season it appears to be in the leading group, though it probably will not qualify for the superfinal.

Interesting games:

Game 1, Stoofvlees - AllieStein: AllieStein opened a file on the queen side, Stoofvlees opened a file on the king side and pushed a pawn to h6. The black king was under threat, AllieStein gave its two rooks for the white bishop pair and the game reached a QRN vs QBN position. The attack wasn't over and Stoofvlees soon had the black king in a mating net. AllieStein was forced to lose material and the game was over.

Game 6, Stockfish - KomodoDragon: Stockfish pushed the black pieces back, KomodoDragon had very little space and the two black bishops could not move at all. Stockfish exchanged queens and opened the queen side, KomodoDragon gave a knight to capture two white passers. The game reached a RBN vs RB position with black 2 pawns up. Stockfish trapped the black bishop and captured a pawn, then forced a bishop trade. There were enough white pawns for a win in a RN vs R ending.

Game 7, Leela - Ethereal: Evals started to increase early, with equal material and most pieces on the board. Leela placed a knight on e5 and slowly increased the pressure on the king side. After exchanging the DS bishops Leela placed all its pieces on dark squares. The engines shuffled for a while and then opened the king side, Ethereal tried to hide its king behind a white pawn. However Ethereal could not protect its king side pawns and it started to lose material as the files opened, mate followed a few moves later.

Game 8, Stoofvlees - ScorpioNN: Stoofvlees gave a rook for a knight and created connected passers on the queen side. The game reached a QB vs QR position with white pawns on a7 and c7. ScorpioNN had an advanced passer in the center, for a while it thought it could hold but then evals started to increase. Stoofvlees captured the rook and the engines cleared all the passers, leaving only two pawns each on the king side. Stoofvlees forced a queen exchange and the bishop vs pawns ending was a win for white.

Game 11, KomodoDragon - Leela: KomodoDragon captured a pawn and created a queen side passer. Evals did not change a lot for a long while, the position opened and Leela regained the pawn. KomodoDragon thought Leela's move 52 was a blunder and its eval jumped. KomodoDragon increased the pressure on the king side while its passer advanced to the 6th rank. A series of exchanges left a RB vs RB position, white two pawns up. KomodoDragon exchanged bishops and pushed two passers to the 7th rank to win.

Game 15, Stoofvlees - KomodoDragon: Stoofvlees had a bishop pair advantage early in the game. It then exchanged a bishop for a knight and created a pawn majority on the queen side. The game reached a RB vs RN position, Stoofvlees lost two pawns but cleared the queen side for two passers. After reducing to a rook ending KomodoDragon sent passers forward as well, both engines queened a pawn at the same time. Material was equal but the white pawns were more advanced, in a queen ending KomodoDragon could not prevent a second queening, giving Stoofvlees the win.

Game 16, ScorpioNN - Ethereal: ScorpioNN went a pawn up on move 19, evals were over 2 by then. The engines reduced to a RRN vs RRB position, ScorpioNN captured two more pawns and slowly pushed its passers forward. Ethereal was unable to stop a queening and lost.

Game 18, KomodoDragon - ScorpioNN: The engines shuffled for a while, then KomodoDragon gave a pawn and attacked the king side. There was a long PV agreement with many exchanges, KomodoDragon opened the king side and chased the black king across the board. The game reached a RBN vs RNN position, KomodoDragon had connected passers on the king side and a rook on the 7th rank. Using checks KomodoDragon managed to promote a pawn to a queen and reduce to a winning Q vs R ending.

Game 20, Stockfish - Leela: Stockfish's eval was close to 2 out of book. The black queen moved forward on the queen side, Stockfish kept its king uncastled in the center without fear. Stockfsh opened the king side and captured a pawn, the white king was barely safe but Leela retreated when it started to feel the pressure on its own king. Leela regained the pawn, the game reached a RRB vs RRB position and Stockfish moved a rook to the 7th rank. Leela could not protect all its pawns, allowing Stockfish to reduce to a winning rook ending. 

Game 27, Stockfish - ScorpioNN: ScorpioNN did not take Stockfish's threat on the king side seriously enough. Stockfish's eval jumped while ScorpioNN's eval stayed below 1. In a R vs BB imbalance Stockfish opened the king side and trapped the black king. Then it pushed a passer on the queen side to the 6th rank. When ScorpioNN realized it was going to lose material it gave up and allowed an immediate mate.

Game 28, Leela - Stoofvlees: see featured game below

Scores after RR1: Stockfish +4, Stoofvlees +2, KomodoDragon Leela +1, AllieStein +0, ScorpioNN Ethereal -2, rofChade -4. Many decisive games, so far Stockfish has 4 wins without loss and rofChade had 4 losses without wins. The other engines are in between, there are 4 engines with positive scores (I include AllieStein) and 2 engines with negative scores.

Game 29, AllieStein - Stoofvlees: AllieStein created a BB vs R imbalance, it was two pawns down but Stoofvlees had tripled pawns. In a QBB vs QR position AllieStein pushed a passer forward, and exchanged queens when the passer was on the 6th rank. The two bishops provided support for the passer, AllieStein lost one bishop but queened the pawn. The game reached a tablebase win 15 moves later. A double white win in this opening.

Game 30, Leela - ScorpioNN: ScorpioNN opened a file on the queen side and moved both its rooks forward. Leela reacted by sacrificing a bishop to open the king side and attack the black king. ScorpioNN gave a rook for a bishop while its king ran to the queen side. Leela continued to attack the back rank, ScorpioNN decided to stop defending and allowed an immediate mate.

Game 31, Stockfish - Ethereal: There were no exchanges after the start while evals increased steadily. Stockfish pushed the black pieces back and they had very little space to move. After a few minor piece exchanges Stockfish opened a file in the center and pushed a pawn to b6. Ethereal protected its b7 pawn and was willing to give a rook for a bishop to keep the pawn safe. The rook was trapped and Stockfish was in no hurry to take it. First it threatened the king side and Ethereal moved its king to the center. Then Stockfish lined its major pieces on the open file before finally taking the offered exchange. Stockfish took over the 7th rank and captured 2 pawns, both engines saw the mate coming.

Game 34, KomodoDragon - Stockfish: The engines gradually exchanged pieces until only RB vs RN were left with white a pawn up. KomodoDragon played the endgame patiently, it took more than 20 moves to capture a pawn on the king side. Then KomodoDragon abandoned its queen side majority and switched to the king side, it created a passer and gave a rook for a knight. The passer was unstoppable and the game was soon over. A double white win in this opening. 

Game 38, Stoofvlees - Ethereal: Ethereal moved its king early, making it difficult for its king side rook to develop. Stoofvlees blocked the king side pawns and trapped the black rook, while Ethereal captured a pawn and created a passer on the queen side. Stoofvlees was stronger on the queen side with an extra rook available, it forced through and exchanged a pair of rooks. Ethereal had to let go of its passer. Eventually Stoofvlees captured a pawn and opened a way out for the black rook. It then reduced to a RB vs R ending 2 pawns up, enough material advantage to win.

Game 39, Leela - KomodoDragon: KomodoDragon kept its king uncastled in the center.  Leela threatened to put a knight to f6, KomodoDragon kept the square protected and gave a rook for a bishop on the other side of the board. Leela gave back the material and created a 3 vs 1 pawn majority on the queen side. A pawn exchange cleared the way for two passers, KomodoDragon gave a bishop for one of them. Leela gained material quickly and the game was soon over. A double white win in this opening.

Game 41, Stockfish - AllieStein: The engines opened the king side, Stockfish found safety for its king by castling long while AllieStein kept its king uncastled. AllieStein didn't see the danger coming, Stockfish doubled rooks and exposed the black king. AllieStein reduced to a QRN vs QRB position but Stockfish had enough power to force a mate.

Game 42, rofChade - Leela: rofChade was a pawn up early, the engines reduced to a RB vs BN ending. It took rofChade forever to find the right move sequence, the game reached a tablebase win on move 103. An unexpected win for rofChade, even if it was a double white win in the opening.

Game 43, KomodoDragon - Stoofvlees: The black king remained uncastled in the center, KomodoDragon attacked from the queen side. A series of exchanges ended the attack in a Q vs BB position, then both engines queened a pawn. Stoofvlees gave one check, but then the two white queens on the back ranks finished the game quickly. A double white win in this opening.

Game 45, AllieStein - Ethereal: The engines mostly shuffled in a RBN vs RNN position with white a pawn up, until AllieStein created a passer on the queen side. AllieStein pushed the passer very slowly, it took 30 moves to get to the 6th rank. Ethereal lost material to stop the passer, reducing to a winning BN vs N ending. It took AllieStein another 50 moves to reach a tablebase win.

Game 48, Leela - Stockfish: Leela exposed the black king early, Stockfish exchanged queens and tried to build a fortress. The engines exchanged pieces and evals increased, the game reached a RBN vs RBN position and Stockfish's pawns were all isolated. Leela created a passer and Stockfish gave a bishop for pawns to stop it. Leela had one remaining pawn but it was unstoppable. The game ended a few moves after Leela queened it. A double white win in this opening.

Game 49, Leela - AllieStein: After a long shuffle evals started to jump, probably AllieStein missed something. Leela opened the king side and moved its queen and a rook forward. AllieStein moved its king away from danger but lost a piece and the game reached a QN vs Q position. Despite having a queen AllieStein could not escape the mating net.

Game 52, KomodoDragon - Ethereal: There were no exchanges after the start except one pair of bishops, evals increased constantly. The engines started to exchange pieces on move 38, after a series of exchanges the game reached a double rook ending. Both engines had a passer but while the white king blocked the Ethereal's passer, KomodoDragon's passer could advance freely. Ethereal's rooks had to defend, KomodoDragon pushed the passer to the 7th rank and exchanged a pair of rooks. KomodoDragon abandoned its passer but captured enough pawns to win.

Game 53, AllieStein - KomodoDragon: AllieStein opened a file on the queen side and moved a rook forward. After clearing most of the queen side the game reached a QRN vs QRN position. AllieStein concentrated on an isolated black pawn on the queen side, after a while it captured the pawn and reduced to a knight ending a pawn up with a passer. The white king came forward, KomodoDragon was forced to block the passer and the white king was free to capture the remaining black pawns. AllieStein was 4 pawns up but in no hurry to win, it played on for more than 30 moves before reaching a tablebase win.

Game 55, ScorpioNN - Stockfish: ScorpioNN had an advantage from the opening but couldn't find a way through the black pawn line. It gave a rook for a bishop and evals came down to 0, Stockfish pushed pawns on the queen side where the white king was, and its eval became negative. ScorpioNN saw the danger too late, its king was exposed and it tried to hide behind a black pawn. Stockfish ended the game with a rook sacrifice and mate. Stockfish won both sides of this opening.

Featured game: Leela - Stoofvlees
Premier division, game 28
Link to game on TCEC

Leela castled long and Stoofvlees chose to keep its king in the center uncastled. Leela blocked the king side and the black rook was almost trapped. After a while Stoofvlees gave the rook for a bishop and two pawns, then Leela sacrificed a knight for two pawns and exposed the black king. Leela had 3 major pieces attacking and Stoofvlees only had pieces to protect its king. 

Stoofvlees tried to hold on, some of its pieces were either pinned directly or couldn't move due to a mate threat. Leela avoided exchanging queens, it managed to double rooks on the g file and most black pieces could not move. Stoofvlees' last try was to offer a pawn and threaten a back rank mate.

Leela didn't fall into the trap of course. The black queen came forward to protect the pawns on the queen side, allowing Leela to create new mate threats. Stoofvlees was forced to give its queen for a rook and the game ended a few moves later.