* Spaniard flirted with shock first-round loss
* American Isner dominates both tiebreaks (adds fresh quotes, recasts)
Champion Rafael Nadal was forced to pull out all the stops and leave John Isner battling for "oxygen" in a 6-4 6-7 6-7 6-2 6-4 win in the French Open first round on Tuesday, his first five-set match at Roland Garros.
The Spanish world No.1 is gunning for a sixth title in seven years in Paris but struggled to cope with the giant American, better known for his record 11-hour epic against Nicolas Mahut at Wimbledon last year than his claycourt pedigree.
Isner almost went down in the record books again for a feat just as amazing having dominated the two tiebreaks but Nadal, who next meets compatriot Pablo Andujar, found another gear to pull away and quieten a restless crowd who sensed a huge shock.
"Really what it came down to is the way he played in the fourth and fifth sets," Isner told reporters.
"I haven't seen tennis like that ever. That's why he's number one in the world and one of the greatest players ever. I mean, that 30-all point in the last game, I needed oxygen after that. I almost collapsed. My legs were dead."
No defending men's champion at Roland Garros has lost in the first round and Nadal was last beaten in his first match in a tournament at the ATP Tour finals round robin in 2009.
He also lost in his opening match at the 2008 Rome Masters, in the second round, and narrowly escaped a shock repeat in a sun-bathed if stunned crowd in Court Philippe Chatrier.
"It was like a penalty shootout," said Nadal, who has lost to rival Novak Djokovic in his last two finals on clay and could struggle to hold onto his crown given the pair's differing form.
"(Isner's) serve is almost unstoppable at the moment. In the tiebreak you play under pressure all the time."
The top seed looked to be cruising when he took the first set and broke early in the second before an inspired Isner hit back with some forceful play to go into the tiebreak on a high.
The American raced into a 4-1 lead with Nadal failing to fire with his explosive forehand and giving up the tiebreak 7-2.
Despite Nadal's affinity with the Paris crowds it was underdog Isner who drew the loudest cheers as he continued to match the Mallorcan on the famous venue.
Nadal was struggling to control Isner's high bouncing serve while Isner showed surprising deftness around the net and barely made a mistake in the middle of the match when the pressure was on.
It was no big surprise when Isner took the third set also on a tiebreak despite the gasps from supporters, journalists and players watching down in the locker room.
But great champions are made of sterner stuff and Nadal did not commit one unforced error in seizing the fourth set as Isner finally wilted.