Federer beat Belgian newcomer Kristof Vliegen 6-1, 6-2, 6-1 to win his first match on the red clay here here since 2001.

And despite lingering doubts about their fitness, 2002 French Open champion Serena, the second seed, defeated Iveta Benesova of the Czech Republic 6-2, 6-2 in 66min as older sister Venus, the fourth seed, simultaneously beat Thailand's Tamarine Tanasugarn 6-2, 6-4 in 1hr 11min.

Serena, who returned from eight months off after knee surgery in March, looked in form despite dropping her serve once in the second set before serving out for the match to love against her 51st-ranked opponent.

Venus, the 2002 runner-up, had been in doubt for the tournament after a left ankle problem forced her to default the German Open final, but she never looked worried by her 55th-ranked Thai opponent depite losing her serve four times including her opening service game.

Serena next meets Russian Maria Kirilenko as Venus takes on Croatia's Jelena Kostanic.

Earlier Wimbledon and Australian Open champion Federer dismissed his 110th-ranked lucky loser opponent in just 1hr 16min.

The Swiss, widely considered the finest player of the current generation, has suffered first round defeats on the slow, red clay of Roland Garros in the last two years.

Bidding to better his previous best, a quarter-final appearance in 2001, Federer next meets Germany's Nicolas Kiefer whom he trails 2-3 in their previous meetings but whom he has never played on clay.

Last year's surprise runner-up Martin Verkerk of the Netherlands, seeded 19, won his opening match 7-5, 6-3, 6-1 against France's Julien Boutter.

The big-hitting Dutchman demonstrated how at home he felt at Roland Garros, slamming down 11 aces on his way to victory over wildcard Boutter.

"It feels like home a little bit," said 25-year-old Verkerk. "It's nice to be back in Paris and I'm enjoying it. If you're a finalist it's never nice to lose in the first round."

German seventh seed Rainer Schuettler was knocked out by Belgium's Xavier Maillse 6-4, 7-5, 6-4.

Former women's champion Mary Pierce, the 30th seed, had little problem dispatching Luxembourg's Claudine Schaul 6-2, 6-3 in 74min on the Philippe Chatrier Centre Court.