Dominic Thiem rated his victory over Rafael Nadal at the Nitto ATP Finals as one of the best performances of his career.

After a brilliant contest full of intensity and explosive shot-making, it was US Open champion Thiem who emerged a 7-6 (7) 7-6 (4) winner to move to within touching distance of the semi-finals.

Victory for Stefanos Tsitsipas over Andrey Rublev on Tuesday evening would send Thiem through before his final group match against the Russian debutant on Thursday.

The Austrian said: "It's definitely one of the better matches I've played so far in my career. I think it came close to the second group match of last year against Nole (Novak Djokovic). I think we both played great tennis. Very, very small things make the difference.

"He was the little bit better player in that first-set breaker but I still won it and, even though Rafa is 100 per cent from the first to the last point, it's very, very important to get that first set against him. It's almost impossible to beat him after losing the first set.

"The second set I think had everything. I played probably the best game of the match to make the rebreak and then another good tie-break. It was a great match which I will remember for a long time.

"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."

Despite losing the match, Nadal was left with positive feelings about his chances of winning a first ATP Finals title.

"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."

Nadal eased past Rublev on Sunday while Thiem was made to work harder in a three-set win over Tsitsipas in a rematch of last year's final.

This match was on another level, though, and the only shame was that there were no fans in The O2 to see it.

Nadal and Thiem had met on 14 previous occasions, all but two of them on clay. The two matches on hard courts were both corkers – a US Open quarter-final in 2018 that Nadal won on a deciding tie-break and a clash at the same stage of the Australian Open earlier this year won by Thiem.

The Austrian won all three of his sets that day on tie-breaks, and the first set here went the same way after 12 pulsating games in which the pair were so well matched that they won exactly the same number of points.

It appeared Nadal would come out on top this time when he led 5-2 with two serves to come but Thiem won both of those points and then, after the Austrian double-faulted, Nadal dumped a snatched backhand into the net on set point.

At 34, the nerves have begun to penetrate Nadal's previously ice-cold veins at the biggest moments, and that was evident again here.

Thiem, who won a long-awaited first grand slam title in New York, now arguably carries the mantle of bravest when the stakes are highest and he saved another set point with a thumping forehand winner before staging a repeat to steal the set.

There was no let-up in quality in the second set, with Thiem responding straight away after Nadal secured the first break of the match in the seventh game.

This time Thiem took hold of the tie-break and did not let go, once again applying full throttle and reaping considerable rewards.