Rafael Nadal missed out on a blockbuster semi-final with Roger Federer despite roaring to his second comeback win of the week at the ATP Finals.

Nadal came from a set down to beat Stefanos Tsitsipas 6-7 (4) 6-4 7-5 in a two hour 52-minute marathon at London's 02.

But it was not enough to set up a mouthwatering clash between the two great rivals, Nadal's opening round-robin match defeat by Alexander Zverev ultimately proving his undoing.

Nevertheless, the 33-year-old got a trophy for his troubles, crowned the year-end world number one, and the eldest man to do it, after Federer's win over Novak Djokovic meant he could not be caught.

Nadal, who won the French and US Opens, said: "I think this trophy is the work of the whole year, a great year in all terms. To have this trophy with me is a big personal satisfaction.

"I think we did a lot of things well during the whole year. Of course the team and the family played a very important role this year, even more than other times because have been some tough moments at the beginning of the season in terms of physical issues that demoralised me a little bit.

"I'm super happy for everything, honestly. To have this trophy with me, with this big gap between the first time until today, 11 years, is a big thing.

"It's something difficult, because 11 years since the first time until the fifth is a big number."

Those five year-end top-ranked finishes moved Nadal level with the achievements of Djokovic, Federer and Jimmy Connors.

"Of course it's important to share five years each with Novak and with Roger," added Nadal, who but for injuries could have already overhauled Pete Sampras' record of six.

"I cannot complain, but at some point I feel that there is a couple of years out there that I have been in a position that I had big chances to be the year number one and I got injured, a long injury," he said.

"So to have the chance to equal both of them after missing a couple of years through injuries means a lot. It's a great achievement."

Nadal was left relying on Daniil Medvedev beating defending champion Zverev if he was to make the last four, a big ask considering the Spaniard's win a few hours earlier had essentially knocked the Russian out, leaving him with only pride to play for.

Medvedev's midweek collapse against Nadal, from 5-1 up and with match point in the deciding set, will be one of the enduring memories from the week by the Thames.

The 23-year-old put up a decent showing against Zverev, but the German has designs on retaining his title and ran out a comprehensive 6-4 7-6 (4) winner.

Zverev will now face Dominic Thiem in Saturday's second semi-final, after Tsitsipas takes on Federer, who will be bidding for a seventh title.