PARIS - Venus Williams bounced back from a poor start at the French Open on Sunday, beating 19-year-old Paula Ormaechea 4-6, 6-1, 6-3 in her first Grand Slam match since revealing she has been diagnosed with an autoimmune disease.

The seven-time major champion seemed taken aback by her opponent's early aggressive play, but still managed to turn the match her way and reach the second round.

The 31-year-old Williams, a former top-ranked player who is now No. 53, is 12-4 this season.

Williams pulled out of the U.S. Open last August before her second-round match, saying she had Sjogren's syndrome, an autoimmune disease that can cause fatigue and joint pain. She returned to the tour in March.

Major champions Sam Stosur and Svetlana Kuznetsova won in straight sets Sunday, quickly making their way into the second round of the French Open on opening day.

The sixth-seeded Stosur, who won last year's U.S. Open and reached the final on the red clay at Roland Garros in 2010, beat Elena Baltacha of Britain 6-4, 6-0 in the first match on the main court.

"It's a bit of an early start, but always nice to get through it now," the Australian said. "You have the whole day and whatever else to recover and, yeah, enjoy."

Kuznetsova won the French Open title in 2009 and the U.S. Open in 2004 but is seeded No. 26 this year. Against Mirjana Lucic of Croatia, she won 6-1, 6-3. The Russian faced little trouble despite being broken twice in the second set.

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No. 10 Angelique Kerber of Germany and No. 20 Lucie Safarova of the Czech Republic also advanced to the second round, along with Americans Melanie Oudin and Irina Falconi.

Former champion Ana Ivanovic beat Lara Arruabarrena-Vecino of Spain 6-1, 6-1.

Ivanovic won her only major title at Roland Garros in 2008, but lost in the fourth round a year later. She fell in the second round in 2010, and then lost in the first round last year.

Against Arruabarrena-Vecino, the former top-ranked Serb had five aces and 27 winners. Arruabarrena-Vecino finished the match with only four winners.

The French Open is the only Grand Slam tournament that starts on Sunday. The other three all start on Monday.

"I don't think it's too big a deal now that it's more of a proper schedule," Stosur said. "I think the first year there was only a handful of matches, and, yeah, if you were on the schedule then, it really didn't feel like the tournament started. Nobody else was thinking that the tournament had started."

Stosur converted five of her eight break points, and briefly allowed Baltacha back into the match by being broken for the first set at 5-3. The Australian broke right back to take the set. In the second set, Baltacha won only four points on her serve, allowing Stosur to advance easily.

Kuznetsova raced through the first set of her match. After leading 3-0 in the second set, Lucic broke twice to get back to 3-3, but Kuznetsova then won the next three games to take the match.

The 30-year-old Lucic reached the Wimbledon semifinals in 1999, but she is now 11-44 against players ranked in the top 30.