Rafael Nadal survived a stern examination of his title credentials to edge out the brilliant Mardy Fish in a late-night classic at the ATP World Tour Finals.
Nadal had not played a competitive match since 13 October and it was all-too apparent as eighth seed Fish fought back from losing the first set to threaten a massive upset.
The crowd at London's O2 Arena were treated to a titanic decider as the clock ticked and both men gave absolutely everything to secure an opening-day win.
Nadal eventually emerged triumphant at 2329 GMT, winning 6-2 3-6 7-6 (7-3) in two hours and 53 minutes of enthralling competition.
The event organisers could not have wished for a better start to the season-ending championship - with Roger Federer's victory over Jo-Wilfried Tsonga also going the distance earlier on Sunday.
But the number of spectators in a capacity crowd that had to leave before the Nadal-Fish match drew to a close will raise questions about the decision to schedule the evening singles matches not before 2000 GMT.
Nonetheless, it made for a thrilling spectacle and Nadal, who required a bathroom break for a stomach problem late on, must now recover in time to play Federer on Tuesday, while Fish takes on Tsonga.
Federer and Andy Murray were among those to predict that Nadal, who took time off to rest after defeat by Florian Mayer in Shanghai, could show signs of rustiness and so it proved.
Fast indoor courts have always been the world number two's least-favourite surface and his preparations were further disrupted when he called the trainer to tape his fingers before play had even begun.
Fortunately for the Spaniard, he was facing a tournament debutant who looked nervous in his new surroundings and three poor errors saw Fish broken to 15 in the opening game.
Nadal was posting an unusually low first-serve percentage but dominating all baseline rallies, and he came out on top after a sensational exchange to move 4-2 ahead before striking again with a forehand winner in the following game.
When the left-hander comfortably served out the set with a nod in the direction of his uncle and coach Toni, it seemed he was heading for a carefree evening.
But if that was the script, nobody had told Fish and, by making greater use of his volleying skills to navigate his own service games, he was able to apply serious pressure on the Nadal delivery.
Nadal went long and wide to put Fish 2-0 ahead in the second set and he almost fell further behind in game six, scrambling all over the court to save two break points for 4-2.
Large sections of the crowd were now pulling for Fish and the American responded with some hugely aggressive tennis, surging to the net at every opportunity.
He forced another four break points in game eight - only for Nadal to hold for 3-5 - before rescuing one himself as he took the match to a third set.
Nadal had won seven of their eight meetings, and that looked certain to become eight of nine when the Spaniard went 2-0 up in the decider with a stunning forehand pass. It was at that point that he left the court for a short time.
However, Fish had nothing to lose and hit straight back with a delicious pick-up that died as it crossed the net, a hold to 15 and backhand winner for 3-2.
With the remaining spectators routinely being brought to their feet, Nadal broke back to love with a forehand pass before both men held for 4-4.
Fish managed to save two match points in game 10 but showed only flashes of his previous brilliance in the tie-break, netting a backhand volley to end a memorable contest.
In the doubles, Mariusz Fyrstenberg and Marcin Matkowski from Poland defeated Michael Llodra and Nenad Zimonjic 6-4 5-7 11-9.