Rafael Nadal began his pursuit of a record-tying 20th men's Grand Slam title with a straight-sets victory at the French Open while Serena Williams made a slow but successful start in her latest bid to equal Margaret Court's all-time mark.
Nadal, 34, needs one more Slam to match Roger Federer's record but has described the defence of his Roland Garros crown as the "most difficult ever" given the cold and damp conditions of a tournament delayed four months by the coronavirus pandemic.
The second seed defeated Egor Gerasimov, the world number 83 from Belarus, 6-4, 6-4, 6-2 to launch his assault on a 13th French Open title, 15 years after triumphing on his debut.
"I am happy, honestly. I did the things that I had to do. I didn't expect much more," said Nadal.
"I'm really happy to be back at Chatrier," he told a smattering of the 1,000 fans permitted daily at Roland Garros.
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"Hopefully it'll be back to normal next year and I'll play in front of the beautiful crowd."
The Spaniard is appearing for the first time in Paris without a clay title to his credit and skipped the recent US hardcourt swing over Covid-19 concerns.
He smacked 32 winners to just 20 unforced errors to down Gerasimov, one of 31 men entered into his first French Open main draw.
"I don't want to make any mistakes. It's a different Roland Garros this year and the weather conditions are very challenging, but we are here to try our best," added Nadal, who faces Mackenzie McDonald in round two.
Williams is chasing an elusive 24th Grand Slam title to draw level with Margaret Court's all-time haul, but clay is her least successful surface.
An error-prone beginning from the American star left world number 102 Kristie Ahn serving for the first set before the three-time Roland Garros champion prevailed 7-6 (7/2), 6-0.
"She played very well in the first set, it wasn't easy for me and she hit a lot of winners," said Williams, playing at the French Open for the 18th time.
"The biggest difference was just confidence. I just need to play with more confidence, like I'm Serena.
"So that was it. I just started playing like that. And I love the clay and I started playing like it, opening the court and moving and sliding."
Williams, seeded sixth here, has not gone beyond the last 16 in Paris since her defeat to Garbine Muguruza in the 2016 final. Her last major came at the 2017 Australian Open while pregnant.
- Medvedev exits early -
Fourth seed Daniil Medvedev crashed out in the first round for the fourth year running, losing 6-4, 7-6 (7/3), 2-6, 6-1 to Hungary's Marton Fucsovics.
The Russian, runner-up at last year's US Open, became the highest-ranked player to fall so far and has yet to win a match at Roland Garros since his debut in 2017.
Italian journeyman Lorenzo Giustino carved out his own place in the headlines when he outlasted France's Corentin Moutet 0-6, 7-6 (9/7), 7-6 (7/3), 2-6, 18-16 in the second longest match in French Open history at six hours and five minutes.
The match, held over from Sunday, fell 28 minutes short of Roland Garros' record marathon tie between Fabrice Santoro and Arnaud Clement in 2004.
US Open winner Dominic Thiem, the runner-up to Nadal in Paris the past two years, defeated former Slam champion Marin Cilic 6-4, 6-3, 6-3.
"My level was good. I was very happy with the way I played from the beginning to the end basically," said Thiem.
Having captured his maiden Slam in New York, Thiem is trying to become the only man in the Open era to win his first two majors at successive tournaments.
"I really love this tournament, it's by far my best Grand Slam tournament so far," said Thiem, who plays American qualifier Jack Sock in the second round.
"I'm from Austria so I know how it is to play in these cold conditions. I love it when it's not too fast."
Eighth seed Gael Monfils, the top Frenchman, lost 6-4, 7-5, 3-6, 6-3 to Alexander Bublik.
Play on Monday was initially delayed by more persistent rain. Petra Kvitova defeated Oceane Dodin 6-3, 7-5 in the only match to start on time under the new roof on Court Philippe Chatrier.
Kiki Bertens overhauled 112th-ranked Ukrainian Katarina Zavatska 2-6, 6-2, 6-0 once conditions improved while Elina Svitolina scrapped past Varvara Gracheva 7-6 (7/2), 6-4.
Garbine Muguruza, the 2016 champion, edged past Tamara Zidansek 7-5, 4-6, 8-6 but last year's runner-up Marketa Vondrousova was bundled out 6-1, 6-2 by Polish teenager Iga Swiatek.