Season 21 premier division, after RR4

Standings after RR4

Stockfish and Leela are in the lead. Stockfish won 6 game pairs and lost one to Leela. Leela won 6 game pairs and drew one against KomodoDragon. KomodoDragon is still in touch with the leaders, only 1.5 points behind.

Ethereal is last after losing 6 game pairs and drawing one against Igel. ScorpioNN and Igel are candidates for relegation, so far their head to head score is a tie.

AllieStein pulled away with 3 game pair wins against the bottom engines, but it hasn't caught up with Stoofvlees yet. Both lost their game pairs against the top engines.

There were 19/28 decisive games in RR3, but only 11/28 in the RR4 reverse games. Only 4/28 game pairs had two white wins despite the opening bias. The top 4 engines beat the bottom 4 engines in 12/16 game pairs in rounds RR3-4, without loss.

Interesting games

game 57, Stockfish - AllieStein: The engines shuffled in a closed position, a few pawn moves and exchanges reset the move counter as the shuffle continued. On move 140 Stockfish's eval started to increase, with less than 20 moves left on the 50-move counter. Stockfish trapped a black rook that moved forward, then used a gap in the wall to move its pieces to the black territory. AllieStein didn't want to lose slowly, it allowed a mate in 1 on the 50th move.

game 59, Leela - Ethereal: The center was blocked, evals started to increase slowly after the position opened a little but still with most pieces on the board. After some shuffling Leela opened a file on the queen side and created a passer on the king side. Ethereal gave a bishop for two pawns to capture the white passer, the engines reduced to a RBN vs RN position. Leela blocked two black passers with its knight, after a bishop for knight trade Ethereal could not block the white passers and the game ended in mate.

game 60, Stoofvlees - ScorpioNN: Stoofvlees sacrificed a knight to open the king side, ScorpioNN built a defensive wall using its pieces and pawns and evals were low. Then ScorpioNN moved a rook forward, this gave Stoofvlees the time it needed to attack the black king and reduce to a R vs B ending. ScorpioNN could not protect its pawns, the game ended in a tablebase win.

game 61, AllieStein - ScorpioNN: The game reached  a QRB vs QRN position with white a pawn up on move 36. Evals were over 1 but for a long time it seemed ScorpioNN had a perpetual check. ScorpioNN regained the pawn and exchanged queens, the engines shuffled and gradually captured pawns. Perhaps ScorpioNN could have held, but something went wrong along the way. In the end ScorpioNN gave its knight to capture the last two white pawns, and surprisingly the result was a 6-man tablebase win in 42 moves for AllieStein in a RB vs R position with one black pawn.  

game 64, Stockfish - KomodoDragon: Evals were around 1 for a long time, Stockfish went up a pawn and it had a bishop pair advantage. After move 40 evals started to increase, the game reached a QBB vs QNN position. It appeared the engines mostly shuffled, though evals continued to increase, on move 60 the queens were off and the white bishops had a clear advantage. Stockfish captured a pawn and created a passer before KomodoDragon traded a knight for one of the bishops. It took another 20 moves to reach a tablebase win.

game 65, KomodoDragon - AllieStein: KomodoDragon sacrificed a knight and exposed the black king, then trapped and captured the black queen for a rook. A series of exchanges reduced to a QB vs RRB position, KomodoDragon gave the bishop and advanced two pawns facing the black king. The white king came forward and AllieStein couldn't avoid mate in the corner.

game 66, Leela - Stockfish: see featured game below

game 67, Stoofvlees - Igel: Evals were under 1 until move 55. The game reached a double rook ending, evals started to increase as the engines played out a long PV agreement where Stoofvlees went a pawn up and a pair of rooks was exchanged. The engines continued to capture pawns and the game ended in a tablebase win.

game 68, ScorpioNN - Ethereal: The center was blocked, evals increased while all pieces were on the board. The first piece exchange was on move 28, the engines shuffled for a while and then ScorpioNN captured a pawn and created a passer on the queen side. ScorpioNN shifted its focus to the king side, a series of exchanges reduced to a QN vs RR position. ScorpioNN captured a rook for a knight, then its queen captured all the black pawns and mate followed.

game 69, AllieStein - Ethereal: Evals increased from the start with very few exchanges. AllieStein had a space advantage, on move 44 Ethereal gave a rook for a knight to avoid further restriction to its movement. AllieStein's eval was in triple digits when the engines opened the queen side and AllieStein pushed a passer to the 7th rank. Ethereal gave a knight to stop the passer, AllieStein was a rook up in a RB vs B position but it took more than 40 more moves to reach a tablebase win.

game 70, Igel - ScorpioNN: Igel pushed pawns on the king side and exposed the black king. SCorpioNN countered with a passer on the queen side, Igel captured the passer and the black rooks moved forward. The black king was left without defenders, Igel mated using a queen sacrifice.

game 71, Stockfish - Stoofvlees: Evals were around 1 from the start with the center blocked and no exchanges. The engines shuffled for 20 moves and Stockfish's eval slowly increased. The engines opened the king side with a few exchanges, Stockfish went a pawn up and Stoofvlees concentrated forces facing the white king. Stockfish defended well, Stoofvlees gave pawns in an effort to involve its knight in the attack. The black king was exposed to attack, Stoofvlees was not fast enough in its attack. Stockfish found an opportunity to strike back and mated.

game 72, KomodoDragon - Leela: KomodoDragon's eval was over 1 from the start, it increased slowly after move 23 as KomodoDragon pushed pawns on the queen side. Leela's eval reacted a few moves later, KomodoDragon opened the queen side, gave a pawn and created a passer on the 7th rank. The black queen was trapped in front of its pawns and Leela traded it for two bishops and a knight. Leela captured the passer but lost a knight, leaving only QR vs RBN. KomodoDragon used the exposed black king to capture pawns, after exchanging rooks the game ended in a tablebase win.

game 73, Leela - AllieStein: AllieStein gave a knight and pawn in an attempt to open the king side and launch an attack on the white king. Evals increased quickly as Leela defended. AllieStein gave a second knight, Leela exchanged pieces and gave the material back to stop the attack. The result was a RBB vs RBB position, Leela captured two pawns and created a passer on the queen side. After exchanging rooks Leela pushed the passer to the 7th rank. AllieStein could not block the passer for long, it promoted to a queen and mate followed.

game 76, Ethereal - Igel: Ethereal had an eval advantage from the start, queens were off early and evals increased steadily. The engines opened the queen side and Ethereal went a pawn up. After a series of exchanges the game reached a RBN vs RR position, Igel with a pawn on the 2nd rank. Igel couldn't keep the passer, after exchanging a pair of rooks the BN vs R was a win for white. It took Ethereal another 30 moves to reach a tablebase win.

game 77, AllieStein - Igel: There were many exchanges after the start and only RB vs RB were left on move 24. After exchanging bishops Igel blundered, the engines exchanged pawns until reaching a winning 7-man position that AllieStein converted.

game 78, Stockfish - Ethereal: Evals jumped over 2 early, Stockfish gave a rook for a knight and created a 6th rank passer on the queen side. Ethereal blocked the passer, this paralyzed its queen side pieces. Ethereal was forced to give the material back, Stockfish shifted to the king side, it gave a knight for 2 pawns and exposed the black king. Ethereal gave material, then its queen gave a series of checks, but mate was unavaoidable.

game 79, KomodoDragon - ScorpioNN: Evals were over 1 from the start, the engines opened the position after a series of exchanges that started on move 17. As a result KomodoDragon was two pawns up with two passers on the queen side while ScorpioNN had a central passer. For a while ScorpioNN thought it was relatively safe, it got a pawn back and pushed its passer to the 7th rank. However evals jumped after KomodoDragon reduced to a RN vs RN position, capturing the black passer and connecting its queen side passers. ScorpioNN still managed to capture a pawn and both engines queened, but KomodoDragon made sure it would exchange queens and reach a tablebase win.

game 80, Leela - Stoofvlees: Stoofvlees gave a pawn early, evals were around 1 until Leela exchanged queens and captured another pawn with a doubled passer in the center. Stoofvlees reduced to a RRB vs RRN position, it captured the doubled passers but remained two pawns down and Leela had a passer on the queen side. The endgame was slow, Leela exchanged a pair of rooks, then it traded its passer for the last black pawn and was left with connected passers on the king side. Stoofvlees could not stop the queening and was mated.

Standings after RR3: Stockfish +7, Leela +5, KomodoDragon +4, Stoofvlees +2, AllieStein -2, ScorpioNN Igel -5, Ethereal -6. In RR3 19/28 games were decisive. Top engines beat bottom engines 8/16 times without loss, and 11/12 within group games were decisive. Stoofvlees and AllieStein now form a small middle group, both losing to top engines and beating bottom engines. The standings will be determined by the reverse games, how many of the game pairs will be decisive and how many will be double wins.

game 88, ScorpioNN - Stoofvlees: ScorpioNN had an eval advantage from the start, the engines opened the position and both had a passer in the center. Stoofvlees gave two pawns and tried to open the center and attack. Evals increased rapidly, ScorpioNN gave back the pawns and the game reached a RBN vs Q imbalance. ScorpioNN used the exposed black king to capture a bishop, then chased the black king across the board. Stoofvlees was forced to give its queen and mate followed. There were two white wins in this opening. This was the first win for a bottom engine against a top engine.

game 90, Stoofvlees - Ethereal: Stoofvlees had an eval advantage even though Ethereal captured a rook for a bishop early. Ethereal was late in developing its queen side, a series of exchanges left a RBN vs RRB position, Stoofvlees with an advanced passer. Eventually Ethereal gave a rook for the passer, after exchanging the remaining rooks Stoofvlees had enough pawns left to win.

game 91, Leela - Igel: There were no exchanges after the start. Leela's eval increased after the engines opened the position and played out a long PV agreement that resulted in a RB vs RN position with white a pawn up. Leela had a passer on the queen side still on the 2nd rank, it took a while until it was ready to push the passer forward. After exchanging rooks Igel moved its king to block the passer, leaving the king side pawns unprotected. The white king cleared the king side and the game ended in a tablebase win.

game 95, Igel - Stoofvlees: Stoofvlees gave a bishop for a pawn, it thought the open g file and threat to the white king were worth the material. Stoofvlees moved its queen forward, the white king was exposed but Igel kept it safe. Stoofvlees realized it was in trouble when Igel created an advanced passer in the center. Igel exchanged pieces and gave the material back to promote to a queen and mate. There were two white wins in this opening.

game 100, Leela - KomodoDragon: Leela's eval increased very slowly as the engines exchanged pieces and opened the position. The game reached a RRB vs RRB position on move 25, the white pieces had more freedom, the black bishop was almost trapped. Leela gave a pawn and created an advanced passer on the queen side. KomodoDragon had unsupported doubled passers, Leela captured both and two more pawns on the king side. KomodoDragon's defense crumbled, it started to lose material and got mated. There were two white wins in this opening.

game 102, KomodoDragon - Stoofvlees: Evals stayed around 1 for a long time, KomodoDragon gave a pawn but its pieces were better placed and the black king was more exposed. On move 40 KomodoDragon moved a rook to the back rank. Suddenly its eval jumped over 5, the engines played a long PV agreement and Stoofvlees thought it was very safe as it counter-attacked the white king without pausing to think. Stoofvlees was blindsighted on move 51, its king was in the center chased by the white pieces. KomodoDragon gained material and mated.

game 103, Stockfish - ScorpioNN: Evals were over 1 from then start, the engines castled in opposite directions and Stockfish pushed pawns on the king side. ScorpioNN went a pawn up but Stockfish had open files to attack the black king and the black pieces were far on the other side of the board. ScorpioNN tried to hold off the attack, it captured another pawn and a rook for a bishop. In the end there were not enough black defenders, the black king ran to the center, Stockfish gained material and mated.

game 104, Igel - Ethereal: The game reached a RRB vs RRN position with white a pawn up. One of the white pawns was doubled and black had a pawn majority on the queen side, evals were over 1. Ethereal decided to move its king to support the queen side, this allowed Igel to cut it off with a rook in the center, evals increased over 2. The white rooks came forward and eventually Igel exchanged a pair of rooks. Ethereal gave a pawn and pushed a passer to the 2nd rank, Igel controlled the promotion square with its bishop. In a series of exchanges Igel gave a rook for a knight and captured the black passer. It had enough pawns to win the B vs R ending. There were two white wins in this opening.

game 107, ScorpioNN - KomodoDragon: The center was blocked with one open file on the king side. Evals increased steadily as the engines played behind the pawn lines and occasionaly exchanged pieces. On move 78 both evals were over 4, KomodoDragon thought that white should give a pawn and attack on the king side. ScorpioNN just shuffled while KomodoDragon waited for an attack that didn't come. This went on until a 50-move draw was reached.

game 110, Leela - ScorpioNN: Leela's eval increased very slowly after the start with very few exchanges. ScorpioNN went a pawn up and tried to attack the white king. Leela kept its king safe, it trapped the forward black queen and evals increased quickly. Leela created a passer on the queen side and went up a pawn. By the time the black queen escaped Leela's PV showed mate.

game 111, KomodoDragon - Ethereal: Ethereal moved its king early and evals increased quickly. KomodoDragon used all its pieces to attack the black king and most black pieces were far on the queen side. KomodoDragon sacrificed a knight and exposed the black king, Ethereal exchanged most pieces and eventually had to give its queen for a rook. KomodoDragon mated using only its queen and pawns.

game 112, Stockfish - Igel: Evals increased quickly after the start. Stockfish attacked the black king and threatened to expose it. Igel exchanged pieces and the game reached a B vs N ending with white a pawn up. Stockfish pushed a passer on the king side and then cleared the queen side pawns with its king. The game ended in a tablebase win.

Featured game: Leela - Stockfish
Premier division, game 66
Link to game on TCEC

For 12 moves after book Stockfish moved only pawns and knights, except for one move with its queen which immediately moved back. Leela had a significant development advantage and evals increased steadily. Starting from move 21 the engines played out a long PV agreement, Leela gave a knight for a pawn to create advanced connected passers on the queen side.

Stockfish pushed its central passer to d4, but could go no further. Eventually Stockfish lost a knight for one passer and the game reached a QRB vs QRB position. Leela captured the black a pawn and created another queen side passer then it exchanged queens.

Leela captured the black passer on d2. Stockfish managed to capture the white passers on the queen side but Leela was busy on the king side and captured two black pawns there. Leela gave the rook to queen a pawn, the game ended in a tablebase win.