World No. 1 Rafael Nadal of Spain met strong challenges from American John Isner and needed to play five sets to go through the first round in the men'singles at the French Open on Tuesday.

The Spanish world number one 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.

At his "second home" at Roland-Garros, Nadal had never before had to play a five setter. Last year, during his triumphant path through the tournament, he had not dropped a single set. Ditto in 2008. Before this match against John Isner, "Rafa" had only lost 10 sets in six appearances in the tournament, and never more than three per edition.

Despite losing the first set, Isner held strong and forced the world number one into a pair of tiebreaks, where his big serve helped him put Nadal on constant pressure.

But with only six unforced errors the rest of the way—none in the fourth set—Nadal proved he is still the man to beat on clay.