Belgium's Steve Darcis, the world No. 135, knocked off No. 5 seed Rafael Nadal of Spain 7-6 (7-4), 7-6 (8-6), 6-4 at Wimbledon on Monday.
The loss marks the first time that Nadal has lost in the first round of a Grand Slam event.
"I had my chances. I didn't make it. So in grass is difficult to adapt yourself, to adapt your game. When you don't have the chance to play before, I didn't have that chance this year, is tougher. I didn't find my rhythm," Nadal said in his post-match interview.
The 27-year-old Nadal was knocked out of Wimbledon by Czech Lukas Rosol in the second round last year.
The Spaniard's loss at Wimbledon last year was followed by a seven-month absence from the ATP Tour due to a knee injury.
Nadal, who won his 8th French Open title on June 9, refused to blame his knee for his loss to Darcis.
"Everything that I will say today about my knee is an excuse, and I don't like to put any excuse when I'm losing a match like I lost today," Nadal said.
The Spaniard, who took the title at the All England Club in 2008 and 2010, has won 12 major championships.
He is tied on the all-time Grand Slam list with Australia's Roy Emerson and trails only American Pete Sampras, who holds 14 major titles, and Swiss great Roger Federer, the winner of 17 Grand Slam singles titles.
Nadal is the only player to win at least one Grand Slam title in nine consecutive years.
In other action on the men's side, Federer, the defending champion and No. 3 seed, defeated Romania's Victor Hanescu 6-3, 6-2, 6-0 on Center Court, while Britain's Andy Murray, the No. 2 seed, beat Germany's Benjamin Becker 6-4, 6-4, 6-2.
France's Jo-Wilfried Tsonga, the No. 6 seed, rolled over Belgium's David Goffin 7-6 (7-4), 6-4, 6-3.
On the women's side, Russia's Maria Sharapova, the No. 3 seed, beat France's Kristina Mladenovic 7-6 (7-5), 6-3 in one hour and 42 minutes, while the Czech Republic's Petra Kvitova, the 2011 champion and No. 8 seed, beat American Coco Vandeweghe 6-1, 5-7, 6-4.
Wimbledon is the third Grand Slam tournament of the season and the only one played on grass. EFE