Topalov, 35, a former world champion who was ranked No. 1 in the world as recently as 14 months ago, has seen his ranking slide to No. 5.

His manager, Silvio Danailov, said in a recent interview with the Web site Chessdom.com that Topalov married a few months ago and was “enjoying life a little bit,” adding, “He is not motivated to play tournaments right now.”

Topalov may also be suffering from a sort of psychological hangover after losing a grueling world championship match in April and May to Viswanathan Anand. He has not really played well since.

His latest setback occurred at the Ajedrez UNAM Quadrangular tournament in Mexico City, which ended a week ago. It was a four-player rapid chess event.

Topalov easily won his semifinal match against Manuel Leon Hoyos of Mexico, 3.5 to 0.5. But in the final against Judit Polgar of Hungary, an opponent he was favored to beat, he was trounced, 3.5 to 0.5. In the last two games, he barely put up any resistance.

In Game 3, Topalov’s sacrifice of rook for knight with 6 Rh5 has been played before and yields White a dangerous attack. Initially, Topalov followed up well, but then he faltered.

Instead of 12 Qh3, he should have played the natural 12 Qf5, when after 12 … e6 13 Qb5 Kd8 14 Qb7 Qc6 15 Qb3, White would have a substantial edge.

Topalov then began to drift. His 19 Nd5 was not as good as 19 Ne4 would have been. And 25 Rf4 instead of 25 Re6 was a mistake. Suddenly, Polgar was in control.

Topalov made his final mistake with 30 Nf3, though 30 Ng2 would have made things even worse.

In Game 4, Topalov was doing fine until he blundered with 19 … Bh5; he should have played 19 … Rad8. After 20 Re5, Topalov had to lose a piece, and he resigned soon afterward because he had no compensation for his material deficit.

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In last week’s column, the analysis of a game between Zhu Chen and Hou Yifan incorrectly stated how the game might have continued. After 25 … h4, it would have been a mistake for Zhu to play 26 Nd8, not 26 Rd8.