After a crushing defeat to Alexander Zverev, Rafael Nadal sought his trademark intensity for his rematch with Daniil Medvedev.

He got his wish.

Nadal saved a match point and rallied from 5-1 down in the final set to defeat the Russian 6-7 (3-7) 6-3 7-6 (7-4) in a near three-hour classic that came two months after his five set, five-hour victory over Medvedev in the US Open final.

"Rafa fought his best, because he could just say, 'Okay, it's over' at 5-1 and just give me the point but we all know Rafa is not about this," Medvedev told reporters.

Nadal's hopes of advancing to the semifinals seemed to be hanging by a thread when Medvedev surged early in the decider but now if he downs Stefanos Tsitsipas on Friday and Zverev loses to Medvedev, the 19-time grand slam winner advances to the last four.

Of the trio of 'Next Gen' stars in Group Andre Agassi, Greece's Tsitsipas booked his spot in the semifinals first by cruising past Germany's Zverev 6-3 6-2 later Wednesday in the night session.

"Today is one of these days, one time of 1,000 you lose this match," Nadal told reporters. "It happened today. Very happy for that, very sorry for him, because to lose a match like this is tough and painful. I feel very sorry for Daniil."

He stopped short, however, of calling it one of the best performances of his career.

"No, no, not at all," Nadal said. "I really hope that I can play better." But "I have been better than the first day."

Nonetheless it was still a miraculous comeback and it means Novak Djokovic must now win the title in London to finish the season as No. 1 ahead of Nadal. Had Nadal lost all three of his round-robin matches, Djokovic would have only needed to make the final.

Djokovic's task became more difficult on Tuesday after his reverse to monstrous hitting Dominic Thiem in another affair that featured a third-set tiebreak to bring the tournament to life.

To reach the last four from Group Bjorn Borg, Djokovic must now beat Roger Federer on Thursday evening in a mammoth contest between Nadal's fellow Big Three members who have amassed a combined 11 year-end titles.

The meeting comes after Djokovic saved two match points in July's Wimbledon final against the Swiss, to the dismay of the majority on Centre Court that day. Federer figures to be the heavy crowd favorite again Thursday at the O2 Arena.

Nadal seeks first title

Nadal has often been beset by injury near the end of seasons and isn't as prolific in these fast indoor conditions but even still, it's incredible to think the newly married 33-year-old has never won the eight-man showpiece.

This time around, Nadal faced a race against time to be fit thanks to an abdominal injury sustained at the Paris Masters. And although he played Monday, he lacked sharpness and was outclassed by the German.

Medvedev said fatigue had caught up with him after a successful but long season and it was evident in the 23-year-old's defeat to Tsitsipas on Monday.

But the 6-foot-6 counterpuncher with the booming serve had enough left to take it to Nadal, having come so close in New York when he fought back from two sets down to force a fifth and almost snatched victory.

The first set in London was a continuation of the high-qualify stuff that featured in New York, with both players hitting double the winners than unforced errors.

There was variety from the baseline, fine net play and rallies that extended to 30 and even 35 shots. The 35-shot rally was pivotal, too, since it went to Nadal as he saved the lone break point of the opener at 3-3 with a looping forehand pass.

Medvedev, though, pulled away in the tiebreak helped by some of those big serves.

The pro-Nadal crowd got an immediate boost -- as did the player -- with a break to start the second and Nadal never relinquished the advantage.

Yet to start the third, it was Medvedev who broke and stepped on the accelerator to lead 5-1. Medvedev had his match point, too, washed away when Nadal struck a half volley drop shot. At the time it felt inconsequential.

At 1-5 "what you think is probably in five minutes you are in the locker room, because that's the normal thing," admitted Nadal. "In that moment, you play with not much pressure because you almost lost."

The third set mirrored the decider in New York, when Nadal led 5-2 before Medvedev pulled to 4-5, only to be stopped there.

More Medvedev misses

As Medvedev missed more and more -- he seemed to feel the pressure attempting to beat Nadal for the first time -- so did his sarcastic thumbs up to his box. The crowd cranked up the noise level.

Medvedev escaped from 0-30 at 5-6 with four huge serves, yet in perhaps the key point of the final tiebreak, he missed a short forehand wide with Nadal stranded at 4-5.

Medvedev then erred wide on a backhand down the line, which was originally called good.

Nadal challenged and to his relief, was proved correct.

It hasn't gone Nadal's way for the most part at the ATP Finals but Wednesday brought respite.