For 20 days the world’s two best grandmasters sat in a soundproof studio in central London, with only a chessboard, their thoughts, and each other for company. But finally, after 15 games, 773 moves and 51 hours of simmering tension, the Norwegian world champion Magnus Carlsen held his nerve, and his crown, with an emphatic rapid-play victory over the US challenger Fabiano Caruana.

Some had wondered whether Carlsen, the world’s No1 ranked player for the past eight years and the world champion since 2013, had lost his mojo because of his diffidence during the classical matches, which were all drawn. Yet over the shorter four-game rapid-play format – where players have just 25 minutes for all their moves, along with a 10-second increment – he was a different animal, crushing his opponent 3-0.

Carlsen defeats Caruana to retain World Chess Championship in tie-breakers – live! Read more

“I am very happy,” a smiling Carlsen admitted afterwards. “I felt like I had a really good day at work. Everything went perfectly.”

Chess has been the sleeper hit of the autumn, with online audiences growing with each passing day despite no decisive results in the 12 classical matches for the first time in the competition’s 132-year history. Naturally the prospect of the first American world champion since Bobby Fischer in 1972 had also attracted a large contingent of US networks to the College in Holborn, all scenting an upset. Carlsen, though, had other ideas.

He visibly relaxed after winning a tricky endgame in the first game, and two more smooth victories ensured he took the winner’s prize of €550,000 (£486,000). Caruana at least had the compensation of returning to St Louis with the €450,000 (£398,000) runners-up prize.

Earlier, Carlsen had appeared pensive as the battery of photographers – who were permitted into the sealed off room for the first three minutes of play – clicked and whirred away. But after Caruana’s third move of the opening game, the unexpected bishop to b4 in the English Opening, Carlsen smiled as if he had been expecting it and instantaneously flashed out his reply.

Both players were behind unidirectional glass, which meant they were unable to see the hundreds of spectators watching on, a necessary precaution in the age of impossibly powerful chess programmes available on mobile phones. But Carlsen’s demeanour made it clear that he fancied his chances in the first game, especially after trading into an endgame where he was a pawn down but had the advantage of the two bishops and his opponent’s fragmented pawn structure.

Those chances only increased after Caruana played his knight to b5 on the 17th move – giving his opponent a massive advantage. However, Carlsen was initially unable to navigate through the tricky waters to victory – a move that would have required him to make an unnatural move with his king to the h1 square – and somehow Caruana looked to have secured a draw.

However, after the American made a mistake on move 34 with barely seconds left on his clock, the Norwegian super computer Sesse was announcing a mate in 39 for Carlsen. It wasn’t so easy to the grandmasters in the press room, but eventually and imprecisely he was able to convert.

For the second game the players once again entered the hyper-aggressive waters of the Sicilian Sveshnikov, as they had done in game eight, 10 and 12. It led to another fascinating position, with Caruana better on the board and ahead on the clock after 17 moves. But Carlsen found a series of first-choice moves before correctly assessing that he could castle when his opponent advanced his pawns on the queenside.

Caruana’s brain scurried back and forth through innumerable tunnels of calculation looking for ways to fight back but after he blundered with knight to d5 on move 28 it was pretty much game over and he was forced to resign one move later.

“I feel that game one was critical for the match,” explained Carlsen later. “It was very tense and it was the breakthrough for me. And in the second I wasn’t sure about my position but after I had won the first game I felt very calm.”

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With Carlsen only needing a draw in the third rapid play he took a cautious approach which led to an equal position. But when Caruana overextended his position in the vain hope of a win, the Norwegian ruthlessly pounced and forced another resignation.

Afterwards the Norwegian also had a sly dig at the former world champions Garry Kasparov and Vladimir Kramnik, who had suggested he had been wrong to offer a draw in a better position in the 12th and final classical game to take the match to a tie-breaker. “I think I made the right decision, and not solely based on the result,” he said. “As for the opinions of Garry and Vlad they are invited to their ‘stupid’ opinions,” he added, smiling.

Caruana, who had played so well in the classical section, admitted to having some “regrets” about not being able to turn good positions into a win. But he admitted that Carlsen had been the better man when it counted. “I was hoping to play my best chess today but I didn’t even come close.”

But despite his loss, his co-manager Mehreen Malik insisted that he had “galvanised” interest in chess in America. “There is a whole generation of Americans who didn’t grow up with Bobby Fischer or interest in this great game, but that has changed in the last three weeks,” she added. “Fabiano went to toe to toe with the world championship, and in doing so has crossed the rubicon into the mainstream. He will be back.”

Indeed he will. But Carlsen, as always, is likely to be blocking his path.