Spain's 12-time champion Rafael Nadal encountered few problems as he started the French Open with a three-set win over Belarusian Egor Gerasimov.
Nadal, 34, wrapped up a 6-4 6-4 6-2 victory in two hours five minutes against the world number 83, who was making his main-draw debut in Paris.
US Open champion Dominic Thiem also moved into the second round with a 6-4 6-3 6-3 win over Croatia's Marin Cilic.
Russian fourth seed Daniil Medvedev is out after losing to Marton Fucsovics.
Thiem, who won his maiden Grand Slam title in New York a fortnight ago, has lost to Nadal in both of the past two finals at Roland Garros.
The pair have been drawn in the same half of the men's singles, meaning they could only meet in the semi-finals this year.
Nadal is seeded second behind Serbia's world number one Novak Djokovic and says the rearranged tournament will provide the "toughest conditions" yet for him.
The 19-time Grand Slam singles champion, who is aiming to move level with Roger Federer's all-time leading men's tally, has only played one clay-court event going into Roland Garros and the cooler conditions are not as beneficial to his game.
Although the scoreline against Gerasimov was comfortable, he was given a decent workout by the Belarusian.
"I'm not going to make a mistake - the attitude and motivation is always here," Nadal said.
"It is a different Roland Garros to the one we are used to and the conditions are very challenging. I'm happy to be in the second round - it is a good start."
American Mackenzie McDonald, ranked 211th, is Nadal's next opponent.
'I'm Austrian so know how to play in these conditions'
Thiem took the upper hand in his match against former world number three Cilic when he broke in the ninth game on his way to sealing the first set.
Cilic, who made 39 unforced errors, was flustered by Thiem's defence, suffering two more breaks in the second set.
Two poor volleys in the sixth game of the third earned the two-time runner-up the crucial break en route to victory.
The Austrian third seed will play American qualifier Jack Sock in the next round.
Thiem, 27, said he was happy he managed a successful transition from playing on hard courts in the heat of New York two weeks ago to performing on clay in damp 13C conditions in Paris.
"I'm from Austria so know how it is to play in cold conditions," he added. "When I was in the juniors I played in 10 degree weather."
What happened elsewhere in the men's draw?
Medvedev is the biggest casualty of both draws so far after losing 6-4 7-6 (7-3) 2-6 6-1 against Hungarian world number 63 Fucsovics.
The 2019 US Open runner-up, who also reached the last four in New York earlier this month, has still not won a main-draw match at Roland Garros after his fourth attempt also ended in misery.
The Russian struggled to adapt his successful hard-court game to the Paris clay once again and his frustrations were clear as he handed over the second set by destroying a racquet on set point.
That landed him a penalty point, after earlier being warned for an audible obscenity, and left him needing to win in five sets for the first time in his career.
Medvedev, 23, clawed a set back but never looked comfortable against a focused Fucsovics, who earned his first top-10 win to reach the second round for the second time.
There were two surprises in the early afternoon matches, with 14th seed Fabio Fognini and Canada's 19th seed Felix Auger-Aliassime dumped out of the competition.
Italian Fognini, 33, suffered a 7-5 3-6 7-6 (7-1) 6-0 defeat by Kazakh former top-50 player Mikhail Kukushkin. And Auger-Aliassime, 20, who reached the fourth round at Flushing Meadows, lost 7-5 6-3 6-3 to Japan's Yoshihito Nishioka.
French number one Gael Monfils, seeded eighth, also went out later on Monday, losing 4-6 5-7 6-3 3-6 to Kazahkstan's world number 49 Alexander Bublik.
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