Playing her first match on a clay court in 15 months, Serena Williams overcame a slow start to advance over fellow American Kristie Ahn.

Despite two breaks of serve in the first set and 28 unforced errors, Serena prevailed 7-6(2), 6-0, to advance to the second round.

“I started out really strong in the first game and I ended up in a tiebreaker,” Williams told Jon Wertheim in her on-court interview. “So I was glad to get through that because she was up a break a couple of times in that first set, but she played really well. She was just striking the ball and not making errors and playing smart.”

Ahn entered the match with just two career wins on a clay court, while the 39-year-old Williams now has 174.

It was a rematch of their first-round encounter at the U.S. Open, won by Williams, 7-5, 6-3.

Serena stands at 23 Grand Slam titles and is seeking to tie Margaret Court’s all-time record of 24 after losing in the U.S. Open semifinals earlier this month.

The first set took 1 hour, 14 minutes, and totaled 102 points. Ahn secured her first break on her sixth breakpoint to go up 2-1 in a game that was nearly 13 minutes long.

She broke again for a 5-4 lead, but Serena broke right back to level the match.

Serena’s movement on clay improved as the first set progressed and she dominated in the tiebreak. She closed out the second set with her 11th ace of the match for her 66th win at Roland Garros. Serena will next play Tsvetana Pironkova of Bulgaria in a rematch of their all-mom U.S. Open quarterfinal, won by Serena in three tough sets.

In the fourth round, Serena could meet Victoria Azarenka, who vanquished her in the U.S. Open semifinals, once again halting Williams’ bid for Major No. 24.

Serena injured her Achilles in that match and then withdrew from last week’s Italian Open. She has been practicing in Paris recently but had issues with the French Open organizers over where she could stay. Tournament officials want all players to stay in one of two mandated hotels, but Serena preferred to stay in her Paris apartment, citing concerns over her lung issues.

“I didn’t want to be in the [official player] hotel because I have lung issues and felt it was a big risk for me personally,” she said. “In a house, I can control more, there’s no housekeeping [staff], none of that stuff. I needed to put my mind at rest so that I could perform in New York.”

If Serena is not pleased with her accommodations during the fortnight, it could complicate her mindset.

“She owns property in Paris, she doesn’t want to stay at the hotel,” Tennis Channel analyst Nicolas Pereira said on air.

“And how she moves in the first rounds, sometimes she gets in trouble there. Until she literally gets her feet under her, she doesn’t feel that comfortable on the clay.”

Of her 23 majors, only three have come in Paris, her lowest total of the four majors. Now she faces a daunting draw while also dealing with the pressure of trying to tie Court. Serena is 0-4 in Slam finals since becoming a mother to daughter Olympia in 2017.

“We’ve been talking about the 24 for so long now and she came out and admitted last year that she was starting to feel that pressure and I felt the fact that she accepted that, I think that helped her a little bit,” Tennis Channel analyst Jill Craybas said.

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