|140th-ranked Stephane Robert of France celebrates his surprise victory over Tomas Berdych [GALLO/GETTY]
Novak Djokovic extended his perfect season into the French Open beating Thiemo de Bakker 6-2, 6-1, 6-3 on Monday in the first round.
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.
"I was serving really, really well and being very aggressive, using every opportunity to step into the court," Djokovic said.
Roger Federer, meanwhile, joined Djokovic in the second round by beating Feliciano Lopez of Spain 6-3, 6-4, 7-6 (3), but sixth-seeded Tomas Berdych was knocked out by French journeyman Stephane Robert in five sets.
On the women's side, top-ranked Caroline Wozniacki eliminated 40-year-old Kimiko Date-Krumm 6-0, 6-2 and defending champion Francesca Schiavone beat Melanie Oudin of the United States 6-2, 6-0.
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.
"That's what can happen in the long matches, and...sadly it happened to me today."
Czech Republic's Tomas Berdych
"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 without facing a single break point against his Spanish opponent.
"Important thing from my side was to be solid in my own serve," Federer said, "which I was all the way through from start to finish."
The third-seeded Federer, who completed a career Grand Slam at Roland Garros two years ago, lost in the quarter-finals last year to end a streak of 23 straight major semi-final appearances.
Berdych, who last year reached the semi-finals at the French Open and the final at Wimbledon, was knocked out by the 140th-ranked Robert 3-6, 3-6, 6-2,6-2, 9-7.
"Maybe it's too early to analyse how was that or what was happening on the court," Berdych said
"That's what can happen in the long matches, and... sadly it happened to me today."
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.
Wozniacki, unbothered by her bandaged left thigh, dominated from the start and won the first seven games in her victory over Date-Krumm.
Date-Krumm made her debut at Roland Garros in 1989, a year before Wozniacki was born. She retired in 1996 and made her return 12 years later.
UK tennis received a welcome boost with 19-year-old Heather Watson becoming the first British woman to win a match at the French Open for 17 years.
Heather beat Stephanie Foretz Gacon 7-6 (8-6) 6-1 inside 96 minutes and is now projected to break the top 100 after the tournament.
The British number three will play Estonian 16th seed Kaia Kanepi in the second round.