Dominic Thiem came out on top in a high-quality match to beat Rafael Nadal at the ATP Finals.
The Austrian won 7-6 (9-7) 7-6 (7-4) for his second victory of the season-ending event at the O2 Arena in London.
Nadal had two set points in the first-set tie-break but could not convert with Thiem eventually securing the win on his fourth match point.
Stefanos Tsitsipas plays Andrey Rublev in Tuesday’s other match of Group London 2020 at about 20:00 GMT.
If defending champion Tsitsipas wins, Thiem will be into the semi-finals before his final match of the round-robin stage.
Nadal will play Tsitsipas on Thursday while Thiem faces Rublev.
“It was a great match from the first to last point. I was pretty lucky to get that first set after being 5-2 down in the tie-break,” Thiem said.
“I had the feeling that the match was a very high level. The atmosphere would’ve been unreal [if fans were in the arena]. We put on a good show for those watching on television.”
Thiem prevails in two gripping sets
Spanish second seed Nadal, who is seeking his first ATP Finals title, and Thiem have brought the best out of each other on many occasions in recent years, with gripping matches at the Australian and US Opens, plus two French Open finals. They did so again here over two hours and 25 minutes when the superb standard barely dropped.
It was such a shame that there was no crowd to enjoy the dazzling shot-making in a first set that went to a tie-break without a break point being created.
Nadal seemed set to take it when he led 5-2 and although Thiem clawed his way back to 5-5, a double fault handed the 34-year-old Spaniard a set point. An uncharacteristic backhand into the middle of the net allowed the Austrian to escape and after Thiem saved another set point, he took his own first opportunity with an inside-out forehand winner.
The first break of the match went Nadal’s way in the seventh game of the second set but 27-year-old Thiem hit back straight away to level at 4-4, before holding serve to put the pressure on the 20-time Grand Slam champion.
Nadal faltered as three errors gave the US Open champion three match points at 0-40 but the Spaniard won the next five points to hold, including a serve-volley at 15-40 that clipped the tape and dropped on his opponent’s side.
The set went into another tie-break and at 3-3, a magnificent backhand winner saw Thiem seize the initiative with the victory secured when Nadal dragged a backhand wide.
It was Thiem’s seventh win in nine matches against top 10 players this year.
“I think that today I played a little bit higher level than at the US Open. It was maybe the best match from me since the restart of the tour and that makes me super happy,” he added.
Nadal said the way he played makes him feel confident for the rest of the tournament.
“It has been a great match of tennis decided for a few small details,” he said. “Just well done to him. He played, I think, an amazing match and I played well too.
“My feeling is not negative. I lost but I had plenty of chances in the first and then I had a break in the second. I think my chances are bigger to have a very good result now than five days ago because the level of tennis, even if I lost today, is much higher.”