Top seed Rafael Nadal created a French Open record for consecutive wins - but admitted he was not at his all-conquering best.
The four-time defending champion was given a thorough work-out by Brazilian qualifier Marcos Daniel, ranked 97th in the world, and came through 7-5 6-4 6-3 to reach the second round.
The 22-year-old made it 29 successes on the trot in the French capital, where he remains unbeaten since making his debut in 2005.
But he was definitely not his usual sprightly self, and even went a break down in the second set.
That proved to be the turning point, though, as Nadal promptly broke back and quickly wrapped up the set.
Daniel, by then resigned to his fate, was broken again at the start of the third set. He managed one last hurrah, breaking Nadal as the Mallorcan served for the match, but he let slip three points to pull it back to 4-5 and a volley that drifted wide sealed his fate.
"It was difficult. I was expecting a hard-fought match but I obviously wasn't at my best level," said Nadal.
"But it's been like that for the last four years (in the first round). And I have won in three sets, that's a positive.
"I started to play better in the third set and I hope to continue improving in the next match."
Roger Federer is probably Nadal's chief rival again this year and he advanced into the second round with a minimum of fuss against Alberto Martin.
The world number two, who is once again bidding to complete his set of grand slams and equal Pete Sampras' record of 14 major titles, eased to a 6-4 6-3 6-2 victory in an hour and 43 minutes.
Earlier, 10th seed Nikolay Davydenko admitted he was not in the best shape to challenge for the title this year, despite a convincing 6-2 6-1 6-4 first-round win over Austria's Stefan Koubek.
The Russian missed the majority of the first three months of 2009 with a heel injury and has recently been troubled by a muscle strain in his left leg that forced him out of last week's Austrian Open.
The two-time Roland Garros semi-finalist knows it will tough for him to match or better his best run here.
"I'm a bit disappointed because I started the clay-court season and I said to myself I was going to be in form for Roland Garros," Davydenko said.
"But after Madrid I injured myself. I couldn't play at Kitzbuhel last week, which prevented me from preparing correctly for Roland Garros.
"I am lacking matches, lacking physical freshness. I don't know what five-set matches are going to do to me."
Fernando Gonzalez, the 12th seed, and Robin Soderling, the 23rd seed, also made it through to round two thanks to three-set wins against Jiri Vanek and Kevin Kim, respectively.
Seventeenth seed Stanislas Wawrinka, of Switzerland, encountered more problems, needing a deciding set to get past Nicolas Devilder 6-3 5-7 2-6 6-4 6-4.
"You never want to think it's over before match point but I knew I wasn't on the right track," said the Swiss, commenting on his feelings when 4-1 down in the fourth.
"But I've always said I liked five-set matches. Physically I feel strong, stronger than most players."
Nicolas Massu, Nicolas Kiefer, Denis Istomin, Mikhail Youzhny and 30th seed Victor Hanescu were other winners today.
Italy's Potito Starace secured a second-round meeting against British number one Andy Murray, the third seed, after opponent Mischa Zverev retired through injury at the start of the third set of their match.
Germany's Zverev was 6-7 (5/7) 7-5 1-0 down when he called it a day because of stomach problems and cramps.