Marin Cilic became the first seed to exit the French Open with defeat at the hands of Ruben Ramirez Hidalgo.
The Croatian 19th seed was beaten 7-6 (7/4) 6-4 6-4 by the Spaniard on the opening day of the tournament.
But there were no upsets for seventh seed David Ferrer who took less than an hour and a half to dispatch Jarkko Nieminen in his opening match.
Cilic, 22, who reached the Australian Open semi-finals, staged a spirited fightback from 5-1 down in the third set.
But clay-court specialist Ramirez Hidalgo, who is ranked 99th in the world, held his nerve to pull off an impressive upset.
Fellow Spaniard Ferrer continued the fine form on clay that has seen him reach finals in Monte Carlo and Barcelona this season, with a comfortable win over Nieminen.
The world number seven eased into the second round with a 6-3 6-3 6-1 victory over the 50th ranked Finn on Court Philippe Chatrier.
Home favourite Jo-Wilfired Tsonga also progressed to the second round in straight sets, but his 6-3 6-2 6-2 scoreline against Jan Hajek flattered the Frenchman slightly.
Both players struggled in windy conditions and 17th seed Tsonga was forced to save break points at the end of the first set before eventually overpowering his opponent.