After nearly a month of fiercely contested play, the World Chess Championship will decide on a series of fast-paced tie-breakers.
Fabiano Caruana since the first US champion since Bobby Fischer in 1972 – but the world number one faces Norwegian Magnus Carlsen.
After 12 draws in 12 regular games, the pair now until a winner is decided on Wednesday.
The ultimate decider can be sudden death game called Armageddon.
That even if the evenly-matched grandmasters fail to be decisive win for one of them, as the time on the clock is quickly pared 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 is far less than the games played so far, where they have a generous hour to begin, with 50 minutes added at turn 40 and 30 seconds per move.
If the pressure is not enough to break one of the contestants, the match format will be "blitz" chess – with just five minutes on the starting clock, and three seconds a move.
Even for the world's two best players, the pressure time can lead to mistakes. They will play up to five sets of two games in this manner.
Then comes Armageddon.
The drawing of lots is a sudden death variant – the player with white pieces gets five minutes on the clock, and black receives only four.
But black has its own advantage.
If, despite the intense speed of the game, it ended again in a draw, the player holding the black king is the winner – and the new world champion.
Whoever is declared the winner will also take home a € 1m (£ 880,000) cash prize.
Defending champion Carlsen appeared to play deliberately for a tie-breaker rather than risk defeat in the 12th and final game of regular play scenario, despite an apparent positional advantage.
"Before the game he decided that draw was what he wanted and even wanted to not go to it," grandmaster Alex Colovic wrote in an analysis piece for Chess.com.
The reason may be simple – while it is 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 has an advantage in fast-paced tie-breakers, but victory is far from certain.
After Monday's offer of a draw, former world champion Garry Kasparov tweeted that he thought the Norwegian was losing his nerve.
Twelve draws in 12 games of regular championship battle – with not a 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 it takes until Armageddon.