The second-seeded Serb improved his 2011 record to 38-0 _ and stretched his winning streak to 40 _ on the second day of the tournament at Roland Garros. And he barely broke a sweat doing it, breaking his Dutch opponent six times.

The 2009 champion Roger Federer, meanwhile, joined Djokovic in the second round by beating Feliciano Lopez of Spain _ but sixth-seeded Tomas Berdych was knocked out by French journeyman Stephane Robert in five sets.

Djokovic walked out onto center court as the co-favorite after beating Rafael Nadal in two clay-court finals leading up to the French Open. He could only meet Nadal in the final at Roland Garros, and if he does he will be assured of taking over the No. 1 ranking from the Spaniard regardless of that result.

"Pressure is always there," said Djokovic, who turned 24 on Sunday. "I know there is a lot of expectations because of the streak I have, but, look, I'm really happy the way I'm handling things right now on and off the court." Djokovic needs five more wins to break John McEnroe's Open era record of 42 for the best unbeaten start, and a sixth victory will make him the first man to win the Australian and French Opens back-to-back since Jim Courier in 1992.

"Coming into a Grand Slam with three titles on clay courts and winning against the best player ever on this surface gives me a lot of motivation, a lot of confidence that I'm trying to use on the court," Djokovic said.

Nadal, who is looking for his sixth French Open title, doesn't get on court until Tuesday, but Federer progressed with a 6-3, 6-4, 7-6 (3) win over Lopez of Spain.

The third-seeded Federer, who completed a career Grand Slam at Roland Garros two years ago, lost in the quarterfinals last year to end a streak of 23 straight major semifinal appearances.

Berdych, who last year reached the semifinals at the French Open and the final at Wimbledon, was knocked out by 140th-ranked Robert 3-6, 3-6, 6-2, 6-2, 9-7.

Berdych held a match point while leading 5-4 in the fifth set, but Robert saved it and went on to earn only his second win at a Grand Slam tournament.

Top-ranked Caroline Wozniacki will also play on the second day of the tournament. The Dane was to face 40-year-old Kimiko Date-Krumm of Japan.

In the opening match on center court, defending champion Francesca Schiavone bounced back to her winning ways by beating Melanie Oudin of the United States 6-2, 6-0.

Schiavone, who last year became the first Italian woman to win a Grand Slam singles title, won four straight games in the first set after being broken early by her 19-year-old American opponent. The fifth-seeded Schiavone, who had 25 winners to Oudin's six, then won seven straight games to reach the second round.

"I'm still shaking a little bit," Schiavone said of playing on Court Philippe Chatrier for the first time as defending champion. "The court is perfect. Everything is going around you and it's like _ you know when you go home and your mom does everything for you and you feel comfortable?" Last week, Schiavone had her best result of the season, reaching the semifinals at the Brussels Open.

No. 3 Vera Zvonareva of Russia, No. 28 Daniela Hantuchova of Slovakia and No. 30 Roberta Vinci of Italy also advanced, while No. 26 Nadia Petrova of Russia, No. 31 Klara Zakopalova of the Czech Republic lost.

In the men's draw, No. 12 Mikhail Youzhny of Russia, No 15 Viktor Troicki of Serbia, No. 23 Thomaz Bellucci of Brazil and No. 25 Juan Martin del Potro all reached the second round.

Del Potro, who won the U.S. Open in 2009, is one of only four Grand Slam champions in the men's tournament, along with Nadal, Djokovic and Federer. The Argentine beat Ivo Karlovic 6-7 (7), 6-3, 7-5, 6-4.

"It's difficult to play against Karlovic, because you don't have many chance to break his serve," Del Potro said of the tall Croat. "I was focused in the beginning to the final, and I got through it."