Williams had few problems in advancing to the second round
Top seed Serena Williams recovered from a stuttering start to reach the second round of the French Open with a 7-6 (7-2) 6-2 win over Stefanie Voegele.
The world number one and 2002 champion saved three break points before edging the first set after struggling to break her Swiss opponent's serve.
But 76th-ranked Voegele was less of a threat in a straightforward second set.
Third seed Caroline Wozniacki and fourth seed Jelena Jankovic each breezed through in straight sets.
Williams has struggled with a knee injury since lifting the Australian Open trophy in January - and had lost two of her last three matches heading into Roland Garros.
Her 20-year-old opponent was the better player for much of the opening set, until American Williams stepped up her game when it mattered in the tie-break, with three service winners.
The second set began with Williams again unable to dictate matters, but she eventually forged ahead with successive breaks before serving out the victory to set up a second round meeting with Germany's Julia Goerges.
"I definitely didn't feel good about it. I'm doing so well in practice, and it just didn't work for me today. At least I won. A different day, a better game, that's how I think about it," said Williams.
Wozniacki, the 2009 US Open runner-up, came into the tournament with some ankle injury concerns as she started off with a 6-0 6-3 win against Russia's Alla Kudryavsteva.
Dressed by Stella McCartney and sporting red nail polish, the 19-year-old Dane took the first set in just 25 minutes.
Wozniacki showed no sign of her recent injury problems
Her opponent finally showed some resistance in the second set, in which she went a break up, but Wozniacki was unfazed as she restored parity, broke for 5-3 and served out to set up a second-round meeting with Tathiana Garbin of Italy.
Her ankle has been a problem since mid-April, but Wozniacki said it had felt "pretty good" during Monday's match in the Paris heat, and added that she enjoyed being one of the leading fancies in a wide-open women's draw.
"You get to play on the big courts, nice crowd. It's just a great thing," she said. "It means that you have done so well throughout the year and you've done so many good results. I'm just happy when I go on court."
Jankovic, a leading contender for this event, defeated Australia's Alicia Molik 6-0 6-4 in a match that finished at nearly 2100 local time.
Twice a semi-finalist, the Serb will face Estonian qualifier Kaia Kanepi for a place in the last 32.
The 2008 champion Ana Ivanovic is unseeded this year having dropped sharply down the rankings through poor form and injuries. But the 22-year-old Serb beat Kai-Chen Chang of Taiwan 6-3 6-3.
Monday proved an excellent day for the seeded women as Elena Dementieva (5), Sam Stosur (7), Agnieszka Radwanska (8), Li Na (11), Lucie Safarova (24), Alisa Kleybanova (28) and Kateryna Bondarenko (32) all went through without dropping a set.
They were joined in the second round by Francesca Schiavone (17), Alona Bondarenko (27) and Alexandra Dulgheru (31), who were all taken to three sets before triumphing.
Meanwhile, Victoria Azarenka has been fined £2,700 for failing to attend a news conference after her first-round loss at Roland Garros.
The 10th seed from Belarus was eliminated on Sunday by Gisela Dulko in a 6-1 6-2 defeat. She had reached the quarter-finals at three of the past four Grand Slam tournaments.