Chess - Borislav Ivanov’s Performance Is Scrutinized - NYTimes.com

But the episode has again raised the question of how officials can monitor games in an era when technology is so advanced, and it set off concerns about how such suspicions will affect the game. If every out-of-the-ordinary performance is questioned, bad feelings could permanently mar the way professional players approach chess.

The player most recently scrutinized was Borislav Ivanov, 25, a low-ranked master from Bulgaria, who won five games, drew two others and lost two at a tournament in Zadar, Croatia. The five victories were against four grandmasters and a strong master, and Ivanov soundly defeated them all.

One of Ivanov’s losses was in a long game in a closed position (the kind where computers perform poorly), and at the end, Ivanov made a rudimentary mistake. It stood out because of how well he had played in the other games. The other loss was in the penultimate round, when the organizers, as a precaution, stopped broadcasting the games on the Internet so that people outside the playing hall could not try to assist the players.

Kenneth Regan, an associate professor of computer science at the University at Buffalo who is also an international master, has spent five years building mathematical models of how players at different levels of skill are expected to perform. The models are based on an analysis of tens of thousands of games.

By comparing tournament results against the models, he comes up with a score of how well players did, move by move, versus how well they were expected to do. He also compares the players’ moves with those of two top-selling computer chess programs.

Regan ran Ivanov’s performance through his system and found that he had the highest move performance score he had ever analyzed — better even than any individual effort by Magnus Carlsen, the player who just rose to the highest chess rating in history, at 2,861.

In an e-mail, Regan wrote that even assuming that Ivanov had a rating of about 2,700, which would make him among the best players in the world, statistically he played well above what a world-class player normally would and more like a computer.

Typical of Ivanov’s games was his victory in Round 6 against Zdenko Kozul, a Croatian grandmaster who is ranked No. 123 in the world.

Though he was Black, Ivanov achieved a slight edge after 11 moves. His 19 ... Nc3 was surprising because after 20 Nc3 dc3, he seemed to have stranded a pawn on c3.

Kozul held up fine until he blundered with 32 Nc5. He overlooked the danger from 32 ... Bg3. He resigned after 34 ... Qf3 because he was about to lose his queen and faced a hopeless endgame.