Novak Djokovic began his campaign for a record 23rd men's Grand Slam singles title with a straightforward victory over Aleksandar Kovacevic.
The Serb, a two-time champion in Paris, defeated the 114nd-ranked American 6-3 6-2 7-6 (7-1).
World number three Djokovic, 36, will face Hungary's Marton Fucsovics in the second round.
"I played well in the first two sets but then I missed opportunities and lost a little focus," Djokovic said.
"But it is also a sign of Aleks' level, which was getting better.
"When you get to a Grand Slam it is not the opponent who gives you the victory, you have to earn it."
Elsewhere on day two, Canada's Felix Auger-Aliassime became the first men's top-10 seed to exit the clay major.
The 10th seed lost 6-4 6-4 6-3 to Italy's Fabio Fognini for his fourth first-round defeat in five years at Roland Garros.
There was victory for another Canadian, however, as Denis Shapovalov battled to a 6-4 7-5 4-6 3-6 6-3 win over American Brandon Nakashima.
Australian 18th seed Alex de Minaur beat Belarusian Ilya Ivashka in four sets, while Spain's 19th seed Roberto Bautista Agut wrapped up a 7-6 (7-4) 6-1 6-1 win over China's Wu Yibing.
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