Tomas Berdych became the first top-10 seed to fall at the French Open when he unexpectedly lost to qualifier Stephane Robert in the first round on Monday.
Czech Berdych, the sixth seed and a semi-finalist last year, was beaten 3-6, 3-6, 6-2, 6-2, 9-7 on Court Two.
Frenchman Robert, who had won only one previous match on the ATP Tour this year, recovered from two sets down and a break down in the decider and saved a match point to book his place in the second round.
"I played my best tennis, I gave everything," Robert told a courtside interviewer after his victory over last year's Wimbledon runner-up in three hours and 23 minutes.
Roger Federer reminded Roland Garros of his extraordinary abilities with a simple 6-3, 6-4, 7-6 win over Feliciano Lopez.
All the talk in the run-up to the year's second Grand Slam had been about how in-form Novak Djokovic could threaten Rafa Nadal's men's crown, but third seed Federer showed he still has a part to play on the Parisian clay.
The 2009 winner needed a break in each of the first two sets to race ahead before triumphing in the tiebreak thanks to the Spaniard netting on his own serve and double-faulting.
The Swiss, who sealed victory with an effortless ace, next meets France's Maxime Teixeira.
Novak Djokovic scorched his way into the second round with a 6-2, 6-1, 6-3 rout of Thiemo De Bakker as his red-hot streak showed no signs of burning out in warm sunshine.
The Serbian, who has never gone beyond the last four on the Roland Garros clay, barely broke sweat in dismissing Dutchman De Bakker.
His 38th straight win since the start of the season and 40th in all was such a formality that his beautifully ironed all-white kit failed to even crease.
"It was a great first match for me at Roland Garros," Djokovic, who celebrated his 24th birthday at the Serbian embassy on Sunday, told a news conference.
"I was serving, really, really serving and being very aggressive. Pressure is always there, over the years you learn how to deal with it.
"I know there is a lot of expectation because of the streak I have but I'm really happy the way I'm handling things right now on and off the court."
Having beaten holder and king of clay Rafa Nadal in finals on the red stuff in Madrid and Rome already this year, Australian Open champion Djokovic is many punters' tip for his first Roland Garros title on June 5.