Lapentti hurt his ankle when coming to net at 5-2 in the first set. He called for a trainer but then continued playing.
The fourth-seeded Djokovic, who won his fourth career title on clay at this month’s Serbia Open, has reached the semifinals at the French Open the last two years. He also won the 2008 Australian Open.
James Blake was the biggest seed to lose so far, falling to a qualifier making his Grand Slam debut.
The 15th-seeded Blake was upset 7-6 (6), 7-5, 6-2 by 93rd-ranked Leonardo Mayer of Argentina.
Blake has never been past the third round at Roland Garros. The American made more than twice as many unforced errors as Mayer.
Fifth-seeded Juan Martin del Potro of Argentina had little trouble in his opening match at Roland Garros, beating Michael Llodra of France 6-3, 6-3, 6-1. Del Potro won four straight ATP titles last year, the first two on clay.
No. 27 Rainer Schuettler of Germany narrowly avoided a “triple bagel” after being shut out in the first two sets of a 6-0, 6-0, 6-4 loss to Marc Gicquel of France.
On Friday, Schuettler lost to Robin Soderling 6-0, 6-0 at the ATP World Team Championship in Germany.
“A ’double bagel’ is fine,” said Schuettler, who reached the semifinals at last year’s Wimbledon. “I had one last week. It’s nothing new.”
Gicquel was unapologetic about the thrashing.
“I didn’t come here to sympathize,” said the Frenchman, who was trying to win the third set at love as well. “If I tried to give him one or two games, then everything could be overturned against me.”
No. 11 Gael Monfils of France also advanced, easily beating Bobby Reynolds of the United States 6-2, 6-3, 6-1 despite being hampered by a knee injury.
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