London's farewell edition of the ATP Finals could still have its dream climax, with world No.1 Novak Djokovic beating Alexander Zverev 6-3 7-6(4) to seal a last-four spot.
After losing to Daniil Medvedev earlier in the week, Djokovic had to beat Germany's Zverev to avoid a group-stage exit and he obliged with a relatively comfortable win.
The 33-year-old Serb will face US Open champion Dominic Thiem in Sunday's semi-final, while world No.2 Rafael Nadal plays Russian Medvedev.
Djokovic was pummelled 6-3 6-3 by an inspired Medvedev, but was much sharper against Zverev, another one of the new generation trying to barge the old guard off stage.
"In contrast to the match against Daniil, I found the right shots at the right time," says Djokovic.
"I have tremendous respect for Sascha, a great player. It was anybody's game for most of the match."
Zverev soundly beat Djokovic in the 2018 final, a match played out in an electrifying atmosphere in front of 18,000 fans. This time, the arena was empty, due to the COVID-19 lockdown, a surreal backdrop for a match with so much riding on it for both men.
Despite the flat feel, Djokovic was quickly into game mode and when world No.7 Zverev double-faulted to drop serve in his first service game, he seized control.
Zverev dug in his heels in the second set, but missed a chance for an early break, before recovering from a couple of double faults to fend off a break point in the following game.
Djokovic looked edgy at times and twice had to hold serve to avoid being dragged into a third set.
But the 17-time Grand Slam champion raised the intensity level in the tiebreak, edging 5-3 ahead with a fizzing backhand pass. He brought up two match points with a hefty first serve, before pressurising Zverev into an error to complete victory.
Djokovic is bidding to equal Roger Federer's record of six ATP Finals titles, while Nadal seeks a first.
Meanwhile, Medvedev was already assured of topping the group after beating Djokovic, but beat Argentina's Diego Schwartzman 6-3 6-3 in their dead rubber.