The four-time defending champion was given a thorough workout by the Brazilian, 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, although he did recover to saunter to victory.
“It was difficult. I was expecting a hard-fought match but I obviously wasn’t at my best level,” Nadal said.
“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 the Swiss 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.
Andy Roddick, the sixth seed, finally got to grips with the Parisian clay, easing past Frenchman Romain Jouan 6-2 6-4 6-2 to pick up his first victory here since 2005.
The other big name in first-round action was 10th seed Nikolay Davydenko, a convincing 6-2 6-1 6-4 winner over Austria’s Stefan Koubek.
Tomas Berdych (19) was the only seed to fall, the Czech losing 6-4 6-4 5-7 4-6 6-3 to Italy’s Simone Bolelli.
Other tight games saw 28th seed Feliciano Lopez come from two sets down to oust Franco Ferreiro 6-7 (3/7) 4-6 7-6 (7/4) 7-5 6-2 and 17th seed Stanislas Wawrinka need a deciding set to get past Nicolas Devilder 6-3 5-7 2-6 6-4 6-4.
Fernando Gonzalez, the 12th seed, and Robin Soderling, the 23rd seed, enjoyed three-set wins against Jiri Vanek and Kevin Kim respectively.
Italy’s Potito Starace secured a second-round meeting with British number one and third seed Andy Murray after opponent Mischa Zverev retired through injury at the start of the third set of their match.
In the women’s, top seed Dinara Safina confirmed her status as title favourite by crushing British number one Anne Keothavong.
While fellow title contender Venus Williams, the third seed, struggled into the second round, Safina provided further evidence she is ready to claim her first grand slam title to justify her world number one ranking.
The Russian ruthlessly saw off Keothavong 6-0 6-0 in 61 minutes on Philippe Chatrier court to set up a meeting with compatriot Vitalia Diatchenko.
Williams was nowhere near as impressive as she claimed a 6-1 4-6 6-2 win over fellow American Bethanie Mattek-Sands.
Maria Sharapova was back in grand-slam action, coming from behind to beat Anastasiya Yakimova 3-6 6-1 6-2. The Russian has not played a grand slam since Wimbledon last year because of a shoulder injury, and her ranking has slipped to 102.
Italy’s Flavia Pennetta, the 14th seed, was a high-ranking casualty, losing 6-1 6-1 to American Alexa Glatch. Elsewhere, 13th seed Mario Bartoli recovered from going a set down to beat fellow Frenchwoman Pauline Parmentier 3-6 6-1 6-3.
Jie Zheng, the 15th seed, eased past France’s Stephanie Cohen-Aloro 6-1 6-3 and Agnes Szavay, the 29th seed, beat Corinna Dentoni 6-3 6-4. Another seed out is Alisa Kleybanova (23), the Russian losing 6-2 4-6 6-1 to Slovenian Polona Hercog.