Medvedev melts down as Nadal storms back to win ATP Finals clash
Medvedev was leading 5-1 in the decisive third set and had match point but threw it away as Nadal rattled off five successive games to take the match into a tie-break, which he won to claim the contest 6-7 (3-7), 6-3, 7-6 (7-4).
The match was a re-run of the pair's epic US Open final which Nadal won, although in London both went into the meeting knowing it was likely make-or-break having lost their opening group encounters, with Nadal being beaten by German youngster Alexander Zverev and Medvedev falling to Greek rival Stefanos Tsitsipas earlier in the week.
A tight first set at the O2 Arena went with serve before fourth seed Medvedev took the initiative in the tie-break, winning it 7-3.
But world number one Nadal fought back to immediately break the Russian at the first opportunity in the second set, going on to take the set 6-3.
It was the 23-year-old Medvedev who seized the first break in the decider as his powerful serving proved increasingly decisive. The 6ft 6in Russian broke Nadal again to set himself up to serve for the match at 5-1, but Nadal showed characteristic grit to save match point and break back to keep himself in the game.
Medvedev continued to appear agitated, giving frequent sarcastic thumbs-up gestures to his team, and the Russian went into full meltdown mode as Nadal incredibly broke again while holding serve to level the set at 5-5.
Nadal took the next game to edge 6-5 in front, although Medvedev finally regained his composure to steady the ship at 6-6 and take the match to a decisive tie-break.
However, Nadal completed his comeback by winning the breaker 7-4 to keep his hopes of a maiden ATP Finals title alive.
Nadal, 33, next meets Greek star Tsitsipas in his final group match as he seeks a semifinal berth, but also knows that he will hold on to the world number one spot should Novak Djokovic fail to win the tournament.
Medvedev next plays Germany's Zverev but knows his hopes of progressing in London are likely to be over, facing a disappointing end to what had been a stellar season for the Russian in which he reached a maiden Grand Slam final and won four titles.
Zverev and Tsitsipas play their round-robin match in Group Andre Agassi at the O2 Arena in the UK capital later on Wednesday.