I have experienced a problem all along during this contest

Garry Kasparov

"I was not outplayed at the board but was completely outprepared," Kasparov said afterwards.

The Russian grandmaster said he wanted a return match with Kramnik when the new champion was ready.

The Beast

Born in Azerbaijan, Kasparov became the youngest-ever world chess champion at the age of 22.

Kramnik: Former protege

Known as The Beast, he had held his title for 15 years, ever since beating Anatoly Karpov in 1985.

His only defeat during that time was by an IBM computer, Deep Blue, three years ago.

But throughout the World Chess Championship at the Riverside Studios in Hammersmith, west London, he appeared to struggle against his fellow countryman.

'Personal problems'

Kasparov said he would give details of personal reasons behind his lacklustre performance once the contest was over.

Kasparov: Baffled and dejected

"It is a long story that I shall reveal later on," he said on Sunday.

Chess experts are puzzled by his loss of form: Kasparov is famously competitive and self-confident, even, some say, arrogant.

Kramnik, by contrast, had been playing strongly and confidently.

He visibly outwitted his former mentor throughout the competition with little-known game strategies and solid defensive play watched by millions as it was broadcast live on the internet.

The two players are obliged to go ahead with the 16th and final game of the tournament on Saturday when they will split the $1.4 million prize depending on the score.