|Venue: O2 Arena, London Date: 15-22 November|
|Coverage: Watch live on BBC Two, BBC iPlayer, BBC Sport website and mobile app; follow BBC radio and live text commentary online on selected matches|
Daniil Medvedev fought back to beat Rafael Nadal and set up a title decider with Dominic Thiem at the ATP Finals.
Nadal served for the match at 5-4 in the second set but the Russian, 24, hit back brilliantly to win 3-6 7-6 (7-4) 6-3 in London.
He was the more aggressive player throughout and was composed in the decider as errors came from Nadal.
Earlier, third seed Thiem beat world number one Novak Djokovic 7-5 6-7 (10-12) 7-6 (7-5) in almost three hours.
The Austrian trusted his big hitting and fought back from a 4-0 deficit in the deciding third-set tie-break to win.
Unlike Thiem, Medvedev, who had never beaten Nadal previously, is unbeaten throughout the week.
Neither man has won the season-ending event before but Thiem will start Sunday’s final as the narrow favourite, having won his first Grand Slam at the US Open in September.
Were world number four Medvedev to win, it would be the biggest victory of his career.
Increased belief helps Thiem rally
Thiem, 27, has stepped up in recent months, winning his maiden Slam and producing some of the best tennis this week in London.
Against Djokovic, his belief in his shot-making and ability to play the big shot at the right moment proved pivotal.
He double faulted on the opening point of the deciding tie-break and Djokovic raced into the lead before Thiem sliced his way back into contention.
A fifth match point was cancelled out by a Djokovic ace but Thiem’s relentless backhand that hugged the baseline was key to his victory.
Djokovic has not been at his best in London and he cut a frustrated figure throughout the decider, letting out a furious yell when he sent an easy return of serve long at 30-30 on the Thiem serve in the third.
His groundstrokes were simply not as consistently composed as usual and his repeated moves to the net did not work.
Usually, a 4-0 lead in a tie-break for Djokovic would mean game over. Instead, he was out-hit and out-thought by his opponent.
“What he did from 0-4 in the third-set tie-breaker was just unreal. I don’t think I played bad. I made all of my first serves. He just crushed the ball,” said Djokovic, who had been chasing a record-equalling sixth title.
“I was in a driver’s position at 4-0. I thought I was very close to winning it. He just took it away from me. But he deserved it, because he just went for it and everything worked.”
Despite the loss, Djokovic finishes the year as world number one, having lost just five matches in 2020, and will now prepare to defend his Australian Open title in January.
More to follow.