The tournament is holding a separate evening session for the first time, emulating the US Open and Australian Open, although for the moment it is behind closed doors because of Paris’ 9pm curfew.
Williams arrived in the French capital with only one victory on clay this season and had some dicey moments against Romania’s Irina-Camelia Begu, particularly when she faced two set points in a first-set tie-break.
But the seventh seed, who had led 5-2, saved both and improved throughout the second set in a 7-6 (6) 6-2 victory.
Williams said: “I’m happy that I was able to save those moments. Did not want to lose that first set. I wasn’t thinking at that moment. I was just thinking to get that ball out the air, because I’ve been hitting some good swing volleys in practice.
“I have to say it was pretty cool to be able to play the first night session ever here at Roland Garros. That was something I thoroughly enjoyed.”
The young Pole produced a stunning run through the draw last year to win her maiden grand slam title and is among the big favourites to lift the trophy again this year.
Swiatek found herself up against her best friend Kaja Juvan in the opening round but there was nothing friendly about the first set as she took it to love – her third 6-0 set in a row after a double bagel against Karolina Pliskova in the final in Rome.
The second set was much closer but Swiatek came through it to win 6-0 7-5, sharing a hug and a debrief with Juvan on the court afterwards.
Swiatek still has a picture of Nadal on her bedroom wall, so Saturday’s practice session between the two reigning champions was something to treasure.
“It was great,” she said. “I had to prepare. Write some small (talk) topics, not to have an awkward silence. But Rafa is really, really great. He’s a really nice guy. Even though I am pretty introverted, it was really fun for me.
“Obviously I got to feel his forehand, which was great, and his topspin. That was a whole new experience for me. It gave me a lot of positive energy. It was really a huge inspiration for me.
“It’s really nice to see such a champion being normal off court, and also telling jokes and being a little bit sarcastic. He’s the guy that everybody can take something from for themselves.”
Having initially found life as a grand slam champion a tough adjustment, Swiatek has embraced her status over the last few months, winning two titles and breaking into the top 10 for the first time.
“You never know what’s going to happen when you’re coming out on a court as a defending champion,” she said.
“I’ve never been in a situation like that. I’m really glad I could handle that pretty well and just play tennis, play a normal match without having in the back of my mind that I’m defending the title.
“It’s never easy to play against your best friend. You just try to block this friendship for two hours, just focus on the game. I think I’m doing that pretty well. It’s nice to have that skill.
“I feel like my game is better and better. My coaches were planning everything for me to have the peak of my shape right now. Hopefully it’s going to be here.”
The first big upset in the women’s draw saw sixth seed Bianca Andreescu lose 6-7 (1) 7-6 (2) 9-7 to Slovenian Tamara Zidansek in an epic contest lasting three hours and 20 minutes.
Canadian Andreescu has been held back by repeated injury problems since winning her first grand slam title at the US Open in 2019 and this was only her second tournament since the beginning of April because of an ankle problem and a bout of coronavirus.
Fourth seed and 2020 finalist Sofia Kenin, who recently ditched her father as her coach, had a very tough draw against former champion Jelena Ostapenko but held firm to win 6-4 4-6 6-3.
There was an upset on Court Simonne-Mathieu where another former champion, 12th seed Garbine Muguruza, was beaten 6-1 6-4 by young Ukrainian Marta Kostyuk, while last year’s semi-finalist Nadia Podoroska went out 6-0 6-3 to 10th seed Belinda Bencic.