London - Rafael Nadal came back from the dead against Daniil Medvedev on Wednesday to keep his ATP Finals hopes alive and boost his chances of finishing as the year-end number one.
The Spaniard was on the brink of defeat when facing a match point after being broken twice to trail 5-1 in the deciding set but stormed back to win 6-7 (3/7), 6-3, 7-6 (7/4).
"Today is one of those days that one out of 1,000 you win and it happened today," said a delighted Nadal.
The Spaniard said earning a break back in the deciding set infused him with confidence that he could battle back.
"When you have the first break, 5-3, then you are only one break away," he added.
"And I know from my personal experience how tough it is to close out matches, especially when you have two breaks in front and you lose the first one. From that moment I thought I can have a chance."
Both players were under intense pressure after losing their opening round-robin matches in Group Andre Agassi on Monday.
Nadal is on a double mission in London -- aiming to win the end-of-season event for the first time in his illustrious career and to secure the year-end number one spot.
Russia's Medvedev, who has won two Masters titles this season, took the first set on a tie-break to leave Nadal staring down the barrel.
The Spanish veteran broke his 23-year-old opponent in the first game of the second set, repeating the trick to level the match.
But Medvedev was quickly into his stride in the decider, sprinting to the net to dispatch a cross-court backhand past his opponent and earn a double break.
Nadal, who came into the tournament under an injury cloud, avoided the embarrassment of a "bagel", which looked a distinct possibility at one stage.
The 19-time Grand Slam champion fended off a match point on his own serve at 5-1 down and then, roared on by the crowd, broke Medvedev twice to level the match at 5-5.
Just when it seemed Medvedev was slipping inexorably towards defeat, he managed to hit the reset button and hold to take the third set into a tie-break.
Medvedev was first to falter in the shootout, hitting a regulation forehand wide to hand Nadal two match points and he grabbed the opportunity.
The Spaniard has qualified 15 straight times for the ATP Finals but has never clinched the title, won a record six times by Roger Federer and five times by Novak Djokovic, battling Nadal for the number one ranking.
In the evening match on Wednesday the two youngest players in the top 10 of the ATP rankings square off, with Stefanos Tsitsipas, 21, taking on defending champion Alexander Zverev, who is 22.
Zverev beat Nadal on Monday for his third consecutive victory at the eight-man ATP Finals against the "Big Three", dating back to last year's tournament.
Tsitsipas defeated Medvedev for the first time in his career.
Dominic Thiem has already secured one of the qualification spots in Group Bjorn Borg, leaving Federer and Djokovic to scrap it out on Thursday for the remaining place from the four-man pool.
Results on the fourth day of the ATP Finals at London's O2 Arena on Wednesday (x denotes seeding):
Group Andre Agassi
Rafael Nadal (ESP x1) bt Daniil Medvedev (RUS x4) 6-7 (3/7), 6-3, 7-6 (7/4)
Stefanos Tsitsipas (GRE x6) v Alexander Zverev (GER x7)
Group Max Mirnyi
Jean-Julien Rojer/Horia Tecau (NED/ROU x6) bt Juan Sebastian Cabal/Robert Farah (COL/COL x1) 6-2, 5-7, 10-8
Kevin Krawietz/Andreas Mies (GER/GER x3) v Pierre-Hugues Herbert/Nicolas Mahut (FRA/FRA x7)