Jannik Sinner came of age at the ATP Finals in Turin with a first career victory over world number one Novak Djokovic.
The 22-year-old Italian won a three-hour marathon 7-5 6-7 (5) 7-6 (2) in a match of high tension and tremendous quality.
Defending champion Djokovic next faces Poland’s Hubert Hurkacz on Thursday in his final group match as he bids to reach the semi-finals.
In front of a raucous home crowd, Sinner grabbed the crucial break in the 11th game, despite finding himself 40-0 down, and then held to love to take the first set.
Djokovic, on a 19-match winning streak, took the second set to a tie-break and was twice a mini-break down before levelling the match, cupping his ear to the spectators.
World number four Sinner then played a stunning return game, breaking Djokovic to 15 with a punishing forehand to move 4-2 up in the third.
But with two hours and 40 minutes on the clock, Djokovic finally broke his young opponent for the first time in the match.
At 5-6 Djokovic began conducting the jeering crowd from his seat at the changeover.
The six-time ATP Finals champion had won 30 tie-breaks this season but number 31 proved elusive as Sinner moved 5-0 up before sealing a statement win with a smash.
“I feel I’m a bit more confident in certain moments but I still have to learn many things,” he said on Amazon Prime.
“I think I was really brave and intelligent, especially in the third set. I think we both played really well.
“It means a lot to me. When you win against the world number one who won 24 grand slams it’s up at the top.”
Djokovic paid tribute to Sinner’s fight in his press conference.
He told reporters: “You have to just congratulate him. He just played a fantastic match. That’s what I told him at the net.
“I think in the most important moments, he played his best game and he absolutely deserved to win.”
The afternoon match ended prematurely when Stefanos Tsitsipas retired after just 15 minutes, handing Holger Rune his first win.
Denmark’s Rune, 20, was leading 2-1 when Greek world number six Tsitsipas pulled out due to a back injury.
Tsitsipas was forced to withdraw from the tournament and was replaced by Hurkacz.
“Unfortunately, I felt terrible on the court. I did what I could do in the best possible way to be ready and fit for this match, but it didn’t work out for me,” Tsitsipas, the 2019 champion, said in his press conference.
“It kills me not to be able to finish this tournament, the one that I’ve prepped for for so long.”
