Big-serving American John Isner produced the first upset at the LA Open with a 7-6, 7-6 victory over seventh-seeded German Benjamin Becker in the opening round on Tuesday.
Isner, who reached his first ATP semi-final of the year in Indianapolis last week, powered down 15 aces before sealing the win in just over two hours on a sun-baked afternoon at the LA Tennis Center.
The towering 24-year-old, 77th in the rankings, swept through the tiebreak in the second set 7-3 to extend his career record to 3-0 over Becker, the world number 44.
"I had a good week last week and maybe I was a little bit tired today," the six-foot-nine Isner told reporters after losing only four points on his first serve. "I played four long matches last week but today was starting off on a good foot."
Isner was heartened to maintain his form after being sidelined from the game earlier this season for just over a month while struggling with mononucleosis.
"It's done now and I've just to get in a little better match shape," he said. "When you take a month off and don't do anything, you lose a lot."
Fifth-seeded Russian Igor Kunitsyn eased into the second round with a 7-5, 6-2 victory over Indian qualifier Somdev Devvarman and Argentina's Leonardo Mayer crushed French qualifier Josselin Ouanna 6-2, 6-3.
In other matches, American qualifier Ryan Sweeting won a fluctuating encounter with compatriot Taylor Dent 6-4, 2-6, 6-3 and Cypriot Marcos Baghdatis, the 2006 Australian Open runner-up, beat Canada's Frank Dancevic 7-6, 6-3.
"I am happy to win my first match here and I feel like I'm playing much better," said former world number eight Baghdatis, whose ranking has plunged to 146th.
"I've been practising really hard and I am trying to get back to my old form."
Australian qualifier Carsten Ball beat Frenchman Marc Gicquel 6-2, 7-6 and Latvian Ernests Gulbis brushed aside Lu Yen-hsun of Taiwan 7-5, 6-2.
Gulbis will next meet either eighth-seeded Russian Marat Safin or American Robby Ginepri, who were playing later on Tuesday.
Top-seeded German Tommy Haas, tournament champion in 2004 and 2006, will launch his bid for a third title at the hardcourt event when he takes on American wildcard Jesse Levine in the second round on Wednesday.