Tennis - ATP World Tour FinalsTennis - ATP World Tour Finals - The O2 Arena, London, Britain - November 13, 2017 Belgium's David Goffin celebrates winning his group stage match against Spain's Rafael Nadal REUTERS/Hannah McKay
By Martyn Herman
Nadal's notorious fighting spirit and Goffin's frayed nerves stretched the match into a third hour but the underdog finally took his chance to claim a first career win over the 16-times grand slam champion.
Spaniard Nadal was moving freely enough for the first half of the match, even if the fizz was missing from his strokes, but by the end he appeared to be playing on one leg as the knee injury that had threatened his participation in the event was clearly causing him pain.
With the year-end number one ranking already in the bag, it would now appear extremely unlikely that Nadal will complete his round-robin matches at the 02.
He is still due to play Grigor Dimitrov and Dominic Thiem.
Eighth-ranked Goffin, the first man from Belgium to qualify for the ATP Finals, seemed to have blown his chance when four match points came and went in the second set, but he broke twice to pull away into a 4-1 lead in the decider.
Again Nadal dug deep to claw back one of the breaks but this time Goffin held his nerve at 5-4 to claim victory with an ace on his fifth match point.
"I'm so glad I found the key to win this match and do it here at the Finals was very special," Goffin, who will be in Davis Cup final action for Belgium later this month, said.
"I just wanted to keep going in the third, even if I lost the second after the match points."
(Reporting by Martyn Herman, editing by Pritha Sarkar)