-- For his 23rd birthday, Andy Roddick got a packed house at Arthur Ashe Stadium, a prime-time TV audience and a date with a 6-foot-5 left-hander from Luxembourg named Gilles Muller. Unfortunately for Roddick, Muller showed up for his U.S. Open debut with a huge serve that was far more effective than Roddick's and a backhand that wasn't nearly as flawed.

The result was a stunning upset that sent the 2003 U.S. Open champion and tournament's fourth seed packing as Muller rolled to a 7-6 (7-4), 7-6 (10-8), 7-6 (7-1) victory before a disbelieving crowd.

It wasn't as if Roddick played poorly. He committed just 15 unforced errors to 39 winners. The outcome was dictated far more by Muller's sterling play -- smartly placed serves, crackling groundstrokes that tagged line after line, and the palpable zeal with which he attacked the ball. Muller, 22, who won the U.S. Open's junior title in 2001 (the year after Roddick), finished with 24 aces to Roddick's 17, while hitting 65 winners and 33 unforced errors.

"For me it was just unbelievable to come out here today," Muller said. "It was first time I am playing night session in a Grand Slam. I told myself before the match, 'Just go out there and enjoy it.' And I did it every minute."

Roddick's defeat will no doubt trigger new rounds of criticism about the lack of variety in his game, which relies heavily on a big serve and booming forehand, and a new wave of soul-searching about the future of American tennis. In the short term, it represents a major blow to the U.S. Open, which in recent years has thrived on the participation and prospects of American stars.

Said Roddick: "I don't really remember a loss where I have felt this bad afterward. I love playing here. I probably had the best practice week I've ever had in lead-up. It just didn't translate tonight. I just felt like the whole time I was trying to find something, as opposed to having it. . . . I'm in a little bit of a shock right now, to be honest."

With Roddick out, those expectations immediately fall on the shoulders of 35-year-old Andre Agassi, who is competing in his 20th U.S. Open.

On the women's side, American hopes ride on second-seeded Lindsay Davenport, who joined sisters Venus and Serena Williams in the second round with her 6-4, 6-4 victory over China's Na Li earlier Tuesday.

Also advancing was defending men's champion Roger Federer, who waltzed past an overwhelmed Ivo Minar of the Czech Republic, 6-1, 6-1, 6-1.

American James Blake scripted the feel-good story of the day with a 7-5, 7-6 (7-3), 6-3 upset of Britain's Greg Rusedski, the tournament's 28th seed.

"I couldn't be happier for him," U.S. Davis Cup captain Patrick McEnroe said of Blake, who saw his world ranking plunge from 22nd to 210th after breaking his neck in a freak accident, losing his father to cancer and contracting a virulent case of shingles last year. "Forget about my position as Davis Cup captain and a fan of American tennis. After all he went through, to see him out there having success, he deserves this. He's such a great kid."

But the day's brightest news for boosters of American tennis was quickly overshadowed by Roddick's swift ouster.

Though he was won four titles this year, including Washington's Legg Mason Tennis Classic, Roddick hasn't posted the results insiders feel he's capable of. He lost in the first week of the French Open and for the second year lost the Wimbledon final to world No. 1 Federer, who extended his record against the American to 10-1 with another victory in the final at Cincinnati two weeks ago.

The question swirling around Roddick on the eve of this year's U.S. Open was whether he would ever figure out how to beat Federer. American Express, one of the tournament's major corporate backers, even built an ad campaign around thinly veiled allusions to Roddick's inability to regain his No. 1 world ranking -- posing the question of whether Roddick would find his "mojo." But the humor of that campaign suddenly felt as flat as Roddick following his stunning defeat.

"Muller was fabulous, but to say this is a shock is an understatement," said CBS commentator John McEnroe, a four-time U.S. Open champion, who expressed bewilderment throughout the match about Roddick's lack of urgency, his ill-advised forays to the net and his inability to get a passing shot by Muller.

It wasn't as if Roddick started poorly. Nor did he lack motivation. Having captured the U.S. Open Series title, Roddick was guaranteed double prize money at this year's tournament -- worth $2.2 million if he won it.

He looked reasonably sharp in the first set, bolting to a 5-2 lead. But Muller stormed back to draw even and force the first of three tie-breakers.

The second set played out much as the first, with Roddick displaying a bit more frustration with each backhand that found the net.

The third set was the same. Roddick changed shirts, but his play was no different. He fell behind quickly in the tiebreaker, as Muller could do no wrong.

In no time Muller's lead was 6-1, and he closed the victory on another netted Roddick backhand.

"I can blame myself because I was in control and I lost it," Roddick said. "To his credit, he raised his level. The bottom line is he stepped up and took the points tonight, and I didn't. I didn't go after them."

Roddick heads back to the practice court, Blake prepares for a second-round match against Igor Andreev of Russia. Up next, should he prevail, is a potential third-round match with second-seeded Rafael Nadal.

Patrick McEnroe believes Blake is more prepared for the battle than at any point in his career.

"As far as the things that frustrated me about his game, he has completely turned that around," McEnroe said. "He plays within himself. He's playing what I call aggressive tennis within the margins. Rather than just cold-cocking his shots and hoping that two out of 10 go in, he sets them up. He doesn't go for the corner; he goes for a space on the court. And he's using his speed around the court. He can run balls down, and he never did that before, even when he got to 22 in the world."

Andy Roddick has nowhere to hide in a 7-6 (7-4), 7-6 (10-8), 7-6 (7-1) loss to Luxembourg's Gilles Muller. "I don't really remember a loss where I have felt this bad afterward."Muller, the U.S. Open junior champion in 2001, is pumped up after winning the second set at Arthur Ashe Stadium.