PARIS -- Her superior serve back at its unreturnable best, Serena Williams was in full control of her French Open match -- until, suddenly, that stroke wasn't as dominant and neither was she.
And then, pushed to a third set by an opponent offering up all sorts of spins and speeds and angles, Williams regained her form and forged to the finish.
Williams got back to the third round at Roland Garros, where she has won three of her 23 Grand Slam singles titles, by pulling away to beat 174th-ranked Mihaela Buzarnescu 6-3, 5-7, 6-1 on Wednesday on Court Philippe Chatrier.
Her serving, especially at the outset, was much better than in her first-round win. In that one Monday, she only put 51% of first serves in play and got broken three times in 10 games.
"I've been practicing my serve a lot. I've been playing, in practice, unbelievable on my serve. The other night was, 'Wooooow,' " she said, rolling her eyes. "I'm glad it came better today. My coach told me it's good that I'm doing it well in practice, because eventually it will be good in the match."
It sure was, especially at the outset against Buzarnescu, who didn't manage to put any serves in play in the first game. By the end of the first set, Williams had won 20 of 23 points she served.
In the second set, things changed.
Buzarnescu made the measure of those powerful offerings and managed to get herself right back in the thick of things, breaking twice in a row.
"She's one of the best servers in the world. It's not easy to read her serve. Being the first time playing against her, it took a while for me to adjust my position in the court on the return," said Buzarnescu, who called it "a dream" to face Williams. "I'm just happy I was able to figure it out. I hope next time, I can do it earlier."
After a bit of a reset, Williams got going back in the right direction.
"I knew going into the third, I just had to zero in on those important points," she said. "If I could just take those, it would be an easier time for me."
Last year, Williams withdrew before the second round in Paris because of an injured left Achilles. No such issues so far this time, and the 39-year-old American covered the court well, although she did have some tape on her right thigh.
Next for the No. 7-seeded Williams is an all-American matchup against Danielle Collins, who overwhelmed Anhelina Kalinina 6-0, 6-2.
It was a strong French Open afternoon for the U.S., including victories in the women's draw for No. 23 Madison Keys and in the men's for No. 31 John Isner, No. 32 Reilly Opelka and unseeded players Stevie Johnson and Marco Giron.
It's the first time that four American men made it to the third round at Roland Garros since a half-dozen got there in 1996 -- and Taylor Fritz still has to play his second match today.
Another American, Tommy Paul, got off to a good start against No. 2 Daniil Medvedev, a two-time Grand Slam runner-up, in the night session Wednesday. But Medvedev, who was 0-4 for his career at the French Open until this week, came back to eliminate Paul 3-6, 6-1, 6-4, 6-3.
Medvedev will take on Opelka for a spot in Week 2.
Earlier in the day, down 4-1 in the third set, 2020 U.S. Open runner-up Alexander Zverev decided it was time to shorten his match.
He was determined to avoid another lengthy fight after a five-setter in the first round, so he applied pressure on qualifier Roman Safiullin. The sixth-seeded German won the next game at love, broke back by pushing his rival into unforced errors and was nearly flawless in the tiebreaker.
The reward was a 7-6 (4), 6-3, 7-6 (1) victory to advance to the third round.
"I'm happy to be through in three sets," Zverev said. "I think it's going to be important for me during the course of this tournament."
Others moving into the third round included qualifier Henri Laaksonen, who hit 53 winners to upset 11th-seeded Roberto Bautista Agut 6-3, 2-6, 6-3, 6-2, and Kei Nishikori, the 2014 U.S. Open runner-up, who was taken to five sets for the second consecutive match before downing the big-hitting Karen Khachanov 4-6, 6-2, 2-6, 6-4, 6-4.
