Qualifier Amer Delic sent seventh seed Carlos Moya out in the second round of the Los Angeles Classic with 14 aces to advance 6-2, 6-7 (5-7) 7-6 (7-5) on Thursday.
The Bosnian-born American, playing in only his fifth ATP event of the season, broke Spain's former number one four times while losing his own serve only twice in a struggle lasting two and a quarter hours.
Moya lost a lead in the final set after salvaging the second set in a tiebreaker against the 26-year-old ranked 137 in a match which ended in a second tiebreak, the dpa reported.
"I lost six points in a row in the tiebreaker - that just doesn't happen," said Moya. "I started slow, but I controlled in the second set.
"In the third I got a bit tired and lapsed. I may have thought the match was almost over but I came back fighting. He served well," said the Spaniard who said the leg problems which have bothered him over the pat month have now subsided.
Moya, 31, last played LA in 2001. He is missing the Olympics where protege and number one-in-waiting Rafael Nadal is looking for a gold medal.
"I think Rafa can stay long at the top ranking," Moya said of the compatriot who takes over on August 18 from Roger Federer. "Maybe not as long as Roger (four and a half years) but a long time.
"This had to be the year that he did it, in a few years there could be a lot more good young players coming up. I think he got the ranking at just the right moment."
Argentine third seed Juan del Potro continued to impress as he earned his 12th straight victory to each the last eight with a 6-4, 6-2 defeat of Italian qualifier Andrea Stoppini.
Del Potro was playing on hardcourt for the first time since collecting Kitzbuehel and Stuttgart clay titles in succeeding weeks.
Stoppini, 221st, has played only three elite-level matches in 2008.
Del Potro advanced in just over an hour, saving seven of the 11 break points.
Frenchman Marc Gicquel of France ended the hopes of teenager Donald Young 6-3, 6-3 two days after the youngster had upset German two-time winner Tommy Haas in the first round.