Three-time defending champion Magnus Carlsen and US challenger Fabiano Caruana face a nerve-wracking showdown in the World Chess Championship in London on Wednesday, after 12 regular games failed to break the deadlock.

The two young masters face off in the 3.00pm (1500 GMT) tie-break, which consists of four rapid matches with 25 minutes for each player with an increment of 10 seconds after each move.

READ| Historical deadlock at World Chess Championship

In case of a tie, they will play up to five mini-matches, each consisting of two blitz games with five minutes for each player and a three-second increment after each move.

If even those tie-breaks are drawn, then it all comes down to one sudden-death “Armageddon” match, with white receiving five minutes and black four minutes.

Black would win automatically in the event of a draw.

Carlsen draws criticism

Norwegian Carlsen, 27, is looking to win a fourth consecutive world title to cement his status as one of the best players of all time.

Caruana, 26, is striving to bring the title back to the US for the first time since the legendary Bobby Fischer beat Russia's Boris Spassky in 1972's “match of the century”, breaking 24 years of Soviet dominance in the middle of the Cold War.

Carlsen and Caruana wrapped up their 12-match series in anti-climatic fashion with a 12th successive draw on Monday, the first time in the tournament's history that all games were tied.

Carlsen will play as white in the first game on Wednesday and excels at rapid chess, making him favourite.

He defended his title through tiebreakers against the Russian Sergey Karjakin in 2016.

“I think I have very good chances,” Carlsen told reporters after Monday's game.

But he came in for criticism for wasting positional and time advantages in the last of the draws, with former Soviet and Russian world champion Garry Kasparov leading the charge.

“In light of this shocking draw offer from Magnus in a superior position with more time, I reconsider my evaluation of him being the favourite in rapids,” he tweeted.

“Tiebreaks require tremendous nerves and he seems to be losing his.”

Caruana said he was “relieved” to still be in the contest after Monday's scare.

“I'm mainly relieved. When you feel like you're sort of on the brink of defeat, or at least you have a very dangerous position, then of course it's quite good.”