Viswanathan Anand retained the World Chess Championship, defeating Bulgarian Veselin Topalov with black pieces in the final classic game of the series in Sofia on Tuesday.

Anand won the 12-game match with a score of 6.5-5.5 to defend the title he claimed in 2007.

A draw in the final game would have taken the match into a series of four rapid games, but Topalov blundered on his 31st and 32nd moves to hand Anand the decisive victory, which came at the end of 56 moves.

The same spirit that saw Topalov adopt the ‘Sofia rule,' under which he refused to accept draw offers, battling till the end before resigning as his position became increasingly untenable.

Anand opted for the Lasker defence after Topalov opened with d4 and black's isolated pawn on c5 was the focus of the early part of the middle game. Anand, however, obtained some counter play with his light bishop that exerted its influence all across the long diagonal from a8 to h1. The position still remained fairly equal until Topalov decided to take black's poisoned pawns on f5 and e4, letting Anand breach his defences in a slightly protracted but ultimately critical manner.

Anand had earlier gotten off to the worst start in the Championship, losing the first game before bouncing back with wins in games two and four. Topalov managed to regain parity with a win in the eighth , but Anand's latest win, the first time that either player had won with black pieces in the series, put an end to the challenge.

Anand won the World Chess Championship in an eight-player tournament in 2007 and defended his title against Vladimir Kramnik in 2008. Topalov won the right to challenge Anand after getting the better of Gata Kamsky in 2009.

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