Ninth seed Gaston Gaudio of Argentina suffered a shock first-round defeat at the U.S. Open on Monday, losing 7-6, 6-2, 6-4 to American wild card Brian Baker, the world number 195.
The former French Open champion was well below his best and Baker took full advantage to record his first victory at a grand slam event and only the fourth win of his career.
"He was better than me today. I didn't do anything," said a rueful Gaudio.
Once the 20-year-old Baker took the first set tiebreak 11-9, Gaudio, the winner of five titles this year, offered little resistance and the American eased to victory in two hours, 29 minutes.
Baker will next play Belgian Xavier Malisse who beat Czech Jan Hernych 6-2, 7-5, 6-2.
"I think I've always had it in me," said Baker. "I just haven't been able to put it together for a whole match. I felt like I played really well and overall it was a great effort out there."
Another Argentine, eighth seed Guillermo Coria, had little trouble beating Spaniard Felix Mantilla 7-6, 6-1, 6-3.
He will meet the winner of the all-American match between qualifier Glenn Weiner and Vince Spadea.
Compatriot and 10th seed Mariano Puerta, runner-up at this year's French Open, beat Noam Okun of Israel 7-6, 6-7, 6-4, 6-0 and now plays either Stanislav Wawrinka of Switzerland or American wild card Rajeev Ram.
Serena too good
Serena Williams overwhelmed Taiwanese teenager Yung-Jan Chan 6-1, 6-3 a women's singles first round match.
The 1999 and 2002 champion's preparations have been hampered by problems with her left ankle and knee and she looked tentative on Arthur Ashe Court against her 16-year-old opponent.
Williams, seeded eighth, appeared more troubled in the first set by the $40,000-worth of diamond earrings she was wearing than her injuries, disposing of them midway through it.
The American trailed 3-1 after losing her serve with a double fault in the second set before reeling off the next five games and capping victory with a delicate backhand drop shot.
"I was playing really flat and lazy so I said, 'Ok Serena let's pick it up and play.' I feel awesome. I feel I have no pressure," the Australian Open champion said.
Serena, who could face older sister Venus in the fourth round, will next play Colombia's Catalina Castano.
Another early winner was Czech 16-year-old Nicole Vaidisova, seeded 26. She overcame compatriot Kveta Peschke 6-3, 6-1.
Fourth seed Kim Clijsters launched her U.S. Open campaign with a 6-1, 6-2 thrashing of German qualifier Martina Mueller.
The in-form Belgian, who has won six tournaments this year, outclassed her 135th-ranked opponent with the punishing baseline shots that have become her trademark.
Clijsters needed only 53 minutes to complete an impressive workout on the Louis Armstrong court, sealing victory with a thunderous first serve.
The 2003 U.S. Open runner-up, who is still seeking her maiden Grand Slam title, will play either Ashley Harkleroad of the U.S. or Colombia's Fabiola Zuluaga in round two.