While Stephens' only Grand Slam title came at the 2017 US Open, she has had sustained success at Roland Garros, finishing as a runner-up to Simona Halep in 2018 and reaching two other quarterfinals on the red clay in Paris, including last year.
"This is my favorite court in the world, so I'm super happy to be back," Stephens told the crowd on Court Philippe Chatrier. "To start a Slam on your favorite court, your favorite surface, is always incredible."
Stephens, who used her postmatch news conference to address the worsening issue of racism in sports, helped American women go 4-0 through the first few hours of play on Day 2 of the tournament after a 1-4 start Sunday, when the only U.S. victory came in a match between two players from the country: Jessica Pegula beat Danielle Collins.
Madison Keys, the runner-up to Stephens in New York six years ago and a semifinalist at Roland Garros in 2018, beat Kaia Kanepi 6-1, 3-6, 6-1 on Monday to improve her career record in the first round of majors to 35-5.
Two-time Grand Slam champion Petra Kvitova, the 10th seed, fell to a 6-3, 6-4 defeat to Italian Elisabetta Cocciaretto, who claimed the biggest win of her career in the opening round. No. 11 seed Veronika Kudermetova also was upset, falling to Anna Karolina Schmiedlova 6-3, 6-1.
Anastasia Pavlyuchenkova, a finalist in Paris in 2021, breezed past Czech teenager Linda Fruhvirtova 6-2, 6-2, No. 12 Belinda Bencic was upset 6-3, 2-6, 6-4 by Elina Avanesyan, 22nd-seeded Donna Vekic beat qualifier Dayana Yastremska 6-2, 7-5, and French favorite Caroline Garcia fought her way into the second round by downing Wang Xiyu 7-6 (4), 4-6, 6-4.
Stephens was down a break in the second set against Pliskova but then won three straight games to close it out. She had a 19-16 edge in winners and committed only 10 unforced errors to 31 by Pliskova, who lost in the finals of the US Open in 2016 and Wimbledon in 2021.
"This court is a bit tricky. You have to play on it a lot to understand when the wind is blowing and where it's coming," Stephens said. "The more you play on it, the more you understand it. But it's a very complicated court. But that's what makes it so amazing."
Stephens won a small clay-court tournament in Saint Malo, France, at the start of the month and reached the semifinals of the Morocco Open last week after playing a total of three matches at bigger clay events in Madrid and Rome.
"Last year, my clay season wasn't great, but I played amazing at Roland Garros last year," Stephens said, "and this year, I really wanted to get matches and play a lot and to see where that got me."
"What I found is a lot, I don't know in a nicer way to say, but a lot of rubbish is happening around the situation where we have to focus on what the main point of what is going on," Svitolina said. "A lot of Ukrainian people need help and support, and we are focusing on so many things, like empty words, empty things that are not helping the situation."
Ukraine's Marta Kostyuk was booed Sunday at the end of her first-round loss after refusing to shake hands with Belarusian Aryna Sabalenka. Belarus has served as a staging ground for Russian troops in the war.
Svitolina, 28, is a former world No. 3 who stopped playing shortly after Russia's invasion of Ukraine last year. She returned to action in April this year following the birth of her first child, winning her first title as a mother at the Internationaux de Strasbourg on Saturday.
"I want to invite everyone to focus on helping Ukrainians, to help kids, to help women who lost their husbands," Svitolina said. "We are missing the main point that people at this time need help as never before. The kids are losing their parents; they are losing parts of their bodies.
"We are missing the main point and talking, talking, talking about nothing."
Pavlyuchenkova said she had feared for her career a year ago because of a knee problem. She said she was forced to go through extensive rehabilitation and stopped playing tennis completely for around five months, with the lack of physical activity during the process leaving her out of shape.
"It was a roller coaster of emotions because I was sad. I was close to crying, but also sad because I wasn't sure what [comes] after," Pavlyuchenkova said after her win. "There were also thoughts, like, 'OK, what if I never come back? Or if I skip that long, because I've never done it. ... What if I never win a match or never be back in good shape? What if that's it?'"
The former world No. 11, who has slipped to 333rd in the rankings, stepped up her comeback with tour-level wins in Madrid and Rome before a run to the Strasbourg quarterfinals. She said she was "super focused" to avoid an early exit at the hands of her young opponent.
"I just focused on my game. I didn't want to lose the first round," Pavlyuchenkova said. "I wanted to stay here as much as possible because it's a very special place for me."
The Associated Press and Reuters contributed to this report.