Muller spoiled what should have been Roddick's 23rd birthday celebrations on the Arthur Ashe Stadium court with a display of poise and precision that left Roddick frustrated at every turn.

Apart from one break in the opening set, which the 22-year-old answered in the ninth game, Roddick couldn't make a dent in Muller's serve.

The left-hander fired 19 forehand winners and seven with his two-handed backhand, keeping Roddick uncharacteristically on the defensive.

Roddick's biggest regret was not serving out the opening set after taking an early break and leading 5-3.

In the second-set tiebreaker, the American had the first set point, which Muller saved with an ace, Roddick responding in kind two points later. Roddick had one more set point at 8-7 in the breaker, but it was Muller who put it away with a backhand passing winner.

Muller, who defeated French Open champion Rafael Nadal in four sets in the second round at Wimbledon, said he benefitted from luck - including a ball hit to the line in the third-set tiebreaker off the frame of his racquet.

Roddick was left to ponder another year without a Grand Slam title, his 2003 triumph here remaining his lone major victory.

Meanwhile world No. 1 Roger Federer took his first step toward in his title defence with a 6-1, 6-1, 6-1 victory over Czech Ivo Minar.

For the second time in as many Grand Slams, Minar found himself serving as early-round Federer fodder, having fallen to the mighty Swiss in the second round at Wimbledon.

After capturing his third straight Wimbledon title - at Roddick's expense - the 24-year-old Federer, 24, is trying to become the first player to defend the US Open title since Australian Patrick Rafter in 1998.

American Lindsay Davenport, the only woman to reach two Grand Slam finals this year, opened her campaign with a 6-4, 6-4 victory over China's Li Na.

Davenport, sidelined for the better part of seven weeks after reaching the Wimbledon final by a bad back, needed four match points to subdue Li.

Women's third seed Amelie Mauresmo advanced with less difficulty, defeating Italian Roberta Vinci 6-3, 6-2.

French Open champion Justine Henin-Hardenne, the seventh seed, routed Czech Zuzana Ondraskova 6-3, 6-0 in 58 minutes.

After missing much of 2004 and the early part of this year battling illness and injury, Henin-Hardenne is climbing back up the rankings and eyeing another Grand Slam title.

She took a long break after a first-round shock at Wimbledon, and said she was ready for the rigors of a Grand Slam challenge.

Last year's beaten finalist - sixth-seeded Russian Elena Dementieva, also advanced with a 7-5, 6-3 victory over Czech Lucie Safarova.

In men's action, 18-year-old qualifier Andrew Murray gutted out a 6-3, 3-6, 3-6, 6-1, 6-4 victory over Romanian veteran Andrei Pavel to keep the British flag flying after the departure of Tim Henman and Greg Rusedski.

Henman, the 12th seed, was clearly hindered by back pain in a 6-4, 6-2, 6-2 loss to rising Spaniard Fernando Verdasco, while Rusedski, seeded 28th, was handed a 7-5, 7-6 (7/3), 6-3 victory by US wild card James Blake.