PARIS — Amanda Anisimova knocked Naomi Osaka out of another Grand Slam tournament on Monday, defeating her, 7-5, 6-4, in the first round of the French Open.

Anisimova, a 20-year-old American with a power game that bears quite a resemblance to Osaka’s, had to save two match points before defeating Osaka in a three-set thriller in the third round of this year’s Australian Open.

But Anisimova was much more efficient on Monday, cracking occasionally under Osaka’s heavy shots and the weight of the moment but ultimately navigating the critical phases of the match with aplomb. Osaka, coming back from an Achilles’ tendon injury, finished with eight double faults and struggled to put first serves in play against Anisimova, a particularly aggressive returner who treats second serves the way a lion might treat a limping impala.

“I think the difference was for me match play, like I only played two matches on clay this year,” Osaka said. “I wish I could have played more. Like I stayed in Europe for longer to be able to prepare for this tournament. So it is a bit disappointing, but I’m happy with how my attitude was, because the last match that we played in Australia I think I was getting a bit more upset with myself.”

Anisimova served out the first set at love, striking three winners, and then served out the victory, finishing off Osaka on her third match point with a cocksure backhand winner down the line that Osaka had no chance to reach.

“When you see Naomi Osaka in the first round, you don’t think it’s going to be easy,” Anisimova said. She added: “Going into the match I did feel the stress and the nerves a bit, because it’s a very tough first round. I’m just happy with how I was able to manage it and get through it.”

Barbora Krejcikova, the reigning French Open champion and No. 2 seed, was also beaten on Monday, upset in the first round by Diane Parry, a 19-year-old French player, 1-6, 6-1, 6-3. Krejcikova had not played a competitive match since February because of a right elbow injury.

She withdrew from preliminary events on clay but played at Roland Garros with her elbow taped and started convincingly against Parry on the main Philippe Chatrier Court before Parry lifted her game. Parry plays with a single-handed backhand: a rarity on the women’s tour. This was her first victory over a player ranked in the top 50, and the French crowd provided plenty of support under the closed roof.

“It’s never easy to to finish a match off on a court like this and against the reigning champion,” said Parry, once the top-ranked junior in the world. She added: “I just told myself to be aggressive and let my shots flow because I have nothing to lose.”

Viewed objectively, Osaka’s loss to Anisimova was no upset. Osaka, a former No. 1 from Japan, is one of the biggest stars in sports and the highest paid female athlete in the world by a large margin. But she has not been a dominant force on tour for well over a year now and has never been a dominant force on the French Open’s clay-court surface.

For now, she remains a one-surface wonder. All four of Osaka’s Grand Slam singles titles were won on hardcourts: two at the Australian Open and two at the United States Open. She has never reached even the final of a clay-court event on tour and has never been past the third round of the French Open. Her career record in singles on hardcourts is 133-56 but on clay it is 21-17 and on grass just 11-9. She said afterward that she was leaning toward not playing next month at Wimbledon, which is played on grass courts, now that the WTA Tour had stripped the event of ranking points in response to Wimbledon’s ban on Russian and Belarusian players.

“I feel like if I play Wimbledon without points, it’s more like an exhibition,” Osaka said. “I know this isn’t true, right? But my brain just like feels that way. Whenever I think like something is like an exhibition, I just can’t go at it 100 percent.”

Last year, struggling on and off court, she withdrew before the second round of the French Open because of a standoff with tournament officials over her refusal to appear at mandatory post-match news conferences. She cited her mental health as the reason for skipping them for as long as she was in the tournament but did not engage with tournament officials directly before announcing her decision or in the aftermath when they sought further explanation. Faced with a lack of background, they fined her $15,000 for missing her first-round news conference and made it clear that she risked being defaulted from the tournament and future Grand Slam tournaments if she continued to refuse to comply with the media requirements.

It was a surprisingly hard line, and Osaka chose to withdraw rather than escalate the situation, revealing as she announced her withdrawal via social media that she had experienced long bouts of depression since winning her first major title at the 2018 US Open.

L’Affaire Osaka at Roland Garros sparked a wide debate on mental health issues in sports and has led to the women’s tour providing even more mental health resources for its players on and off site. Osaka has said that she would like to have handled the situation differently. The French Open has changed some of its leadership, with longtime tournament director Guy Forget being replaced this year by Amélie Mauresmo, a former No. 1 player on the women’s tour who has made players’ mental health a priority. Under her leadership, the French Open has reduced access to player areas for reporters this year. The tournament also is providing mental health experts on site to assist players.

Mauresmo made an effort to greet Osaka on and off court when she returned to Roland Garros this year. Osaka arrived unseeded and having played just two singles matches on clay all year after withdrawing from the Italian Open earlier this month because of her left Achilles’ tendon injury.

Her lower left ankle was taped on Monday for the rematch with Anisimova, the No. 27 seed, who as the higher ranked player, walked on the Suzanne Lenglen Court after her opponent.

Osaka said she took painkilling medication before taking the court. “I still kind of felt it a little,” she said. “I’m going to see what happens when it wears off.”

The ball striking was ferocious from the opening point. Though conditions were humid and heavy on the clay, Anisimova and Osaka both have the punching power to hit winners in any conditions. But Anisimova, tall and with a taste for risk, has had a lot more success at Roland Garros so far than Osaka. As a 17-year-old, Anisimova reached the semifinals in 2019 before losing to eventual champion Ashleigh Barty.