Fourth-seeded Grigor Dimitrov found out about his French Open opponent about 30 minutes before stepping onto Court Philippe Chatrier but had no problem adapting to the situation.
Dimitrov, a semifinalist at Monte Carlo this season, was slated to play Viktor Troicki but instead faced Mohamed Safwat of Egypt because Troicki withdrew with pain in his back. Dimitrov hit 31 winners and prevailed 6-1, 6-4, 7-6 (1).
"I just needed, like, five, 10 minutes to disconnect from what I had in mind to play and what I wanted to do and kind of look at the few videos of the way he was playing," Dimitrov said. "After that, I just had to go out and do the best that I can. I think it was a good start."
Safwat, the first Egyptian man to compete at a Grand Slam since Tamer El Sawy at the 1996 US Open, was cheered off the court.
Gael Monfils, one of six Frenchmen in action on Sunday, overcame a slow start and an upset stomach and headache to advance by defeating compatriot and wild card Elliot Benchetrit. Monfils won 3-6, 6-1, 6-2, 6-1.
"I was stressed and even sick at the beginning," Monfils said. "Then experience played in my favor."
Kei Nishikori made light work of his first Grand Slam match since Wimbledon last year with a 7-6 (7), 6-4, 6-3 win against wild card Maxime Janvier of France.
Nishikori, a 28-year-old from Japan, is seeded 19th at Roland Garros. After appearing in 21 consecutive Grand Slam tournaments, he missed two in a row -- last year's US Open, then the Australian Open this January -- because his right wrist was not fully recovered enough from a torn tendon.
In a clash between the youngest and oldest players in the men's draw at the French Open, the youngest prevailed on remote court 7.
Playing at Roland Garros with a wild card, 19-year-old Frenchman Corentin Moutet defeated veteran Ivo Karlovic 7-6 (7), 6-2, 7-6 (5) to reach the second round.
At 39 years, 88 days, Karlovic is more than 20 years older than Moutet, one of the six teenagers in the main draw at Roland Garros.