After nearly a month of fiercely contested play, the World Chess Championship will be decided by a series of fast-paced tie-breakers.
Fabiano Caruana hopes to become the first US champion since Bobby Fischer in 1972 – but faces the world's number one Norwegian Magnus Carlsen.
After 12 draws in 12 regular games, the pair now face ever-tighter time limits until a winner is decided on Wednesday.
The ultimate decider could be the sudden death game called Armageddon.
That will only happen if the evenly-matched grandmasters fail to make a decisive win for one of them, as the time on the clock is quickly parsed down.
Starting at 15:00 GMT in London, Caruana and Carlsen will play four games with just 25 minutes on each player's timer at the start and 10 seconds added per move.
That's far less than in the games played so far, where they have had a generous hour to begin, with 50 minutes added at the turn of 40 and 30 seconds per move.
If that pressure is still not enough to break one of the contestants, the match format moves to the "blitz" chess – with only five minutes on the starting clock and three seconds a move.
Even for the world's two best players, tight time pressure can lead to mistakes. They will play up to five sets of two games in this way.
Then comes Armageddon.
The drawing of lots is crucial in this "sudden death" variant – the player with white pieces gets five minutes on the clock, and black receives only four.
But black has his own advantage.
If, despite the intense speed of the game, it once again ends in a draw, the player holding the black king is declared the winner – and the new world champion.
A winner will also take a € 1m (£ 880,000) cash prize.
Defending champion Carlsen seemed to play deliberately for a tie-breaker in the 12th and final game of regular play rather than risk defeat, despite the apparent positional advantage.
"Before the game he decided that draw was what he wanted and even when something more was possible he did not want to go for it," grandmaster Alex Colovic wrote in an analysis piece for Chess.com.
The reason may be simple – while Carlsen and Caruana ranked number one and two in the world for regular play, that's not the case for fast-paced blitz chess.
There, Carlsen remains the world's top ranked player – but Caruana drops to spot number 18.
It is not unreasonable for Carlsen to think he may have a benefit in the fast-paced tie-breakers, but the victory is far from certain.
After the Monday's offer of a draw, former world champion Garry Kasparov tweeted that he thought the Norwegian was losing his nerves.
Twelve draws in 12 games of regular play is a record for a championship battle – with no single victory in regular play.
"The match has made history, though of an ignoble kind," the World Chess broadcast's tournament report said, reflecting the frustration of some viewers after so many draws.
But Wednesday's game structure means that no matter what, there will be a new champion – even it takes until Armageddon.