New York - More than an hour after hitting one last shot as a professional tennis player, then delivering one last, voice-wavering speech to an adoring U.S. Open audience, Andy Roddick exited the locker room one last time.

Accompanied by his wife and other family members, a black baseball cap tugged low over his eyes, Roddick slung a racket bag off his aching right shoulder - the one responsible for so many high-speed aces, violent forehands and the most recent Grand Slam title by an American man - and tossed the equipment in the back of a waiting van.

Won't need that any longer.

Serenaded by choruses of "Let's go, Andy!" that rang through Arthur Ashe Stadium in the closing moments of his career, the 2003 U.S. Open champion headed into retirement with a 6-7 (1), 7-6 (4), 6-2, 6-4 loss to 2009 champion Juan Martin del Potro of Argentina in the fourth round at Flushing Meadows on Wednesday.

"If we do badly, then it costs us something; if we do well, we get great things. This was about something bigger. It wasn't about ranking points or paychecks or anything else," Roddick said. "This week I felt like I was 12 years old, playing in a park. It was extremely innocent. That was fun. I enjoyed it."

It was a bittersweet goodbye, for the fans who gave him a standing ovation at the end - del Potro joined in, rising from his changeover chair to applaud - and for Roddick himself.

He covered his face with a white towel while seated on the sideline after sailing a running forehand long with the final swing of his racket. Earlier, he appeared to be trying to avoid crying while serving in the next-to-last game; in the stands, his wife, model-actress Brooklyn Decker, stuck a finger underneath her dark sunglasses to wipe away her tears.

"Playing the last five games was pretty hard. Once I got down a break, I could barely look at my (guest) box," Roddick said during a news conference sprinkled with the sort of witty one-liners he quickly came to be known for after turning pro in 2000. "I don't know what the emotions are. I'm a little overwhelmed right now. I normally feel like I can grasp things pretty quickly and clearly. I certainly don't feel that way right now."

During an on-court address to the crowd, Roddick got choked up, particularly when making a reference to his longtime agent, Ken Meyerson, who died last year.

When handed a microphone, Roddick began by saying: "Oh, wow. For the first time in my career, I'm not sure what to say."

"Since I was a kid, I've been coming to this tournament. I felt lucky just to sit where all of you are sitting today, to watch this game, to see the champions that have come and gone," Roddick told the fans in a moment reminiscent of Andre Agassi's farewell speech at the 2006 U.S. Open after his final match. "I've loved every minute of it."

Roddick finished with a record of 612-213 (a winning percentage of .742). He won 32 tournament titles, led the United States to the 2007 Davis Cup championship, and injected a say-what-you-think personality into his sport.

Del Potro's quarterfinal opponent will be defending champion Novak Djokovic, who advanced when No. 18 Stanislas Wawrinka stopped playing Wednesday because of illness and fatigue while trailing 6-4, 6-1, 3-1.

Djokovic's Serbian Davis Cup teammate, No. 8 Janko Tipsarevic, finished his rain-interrupted 6-3, 7-6 (5), 6-2 victory over No. 19 Philipp Kohlschreiber of Germany, and gets No. 4 David Ferrer of Spain in the quarterfinals.

Olympic champion Andy Murray was the first man into the semifinals, turning things around after being a point from a two-set hole against 12th-seeded Marin Cilic and winning 3-6, 7-6 (4), 6-2, 6-0. Next for Murray will be a match against 17-time major champion Federer - the man the Brit lost to in the Wimbledon final in July, then beat for a gold medal at the Summer Games in August - or No. 6 Tomas Berdych.

Like Murray, four-time major champion Maria Sharapova constructed quite a comeback in her quarterfinal, erasing a 4-0 deficit and defeating 2007 Wimbledon runner-up Marion Bartoli 3-6, 6-3, 6-4. Sharapova is 12-0 in three-set matches this season.

"It's a great statistic," Sharapova said. "It shows that I enjoy the battle, no matter what the score is."

No Sharapova-like or Murray-esque theatrics were required by Serena Williams, who has won three of her 14 Grand Slam titles at the U.S. Open. She hit 12 aces in her latest dominant performance, a 6-1, 6-3 victory over 2008 French Open champion Ana Ivanovic.

Williams' semifinal opponent will be 10th-seeded Sara Errani of Italy, who eliminated her good friend and doubles partner, No. 20 Roberta Vinci, in straight sets.

The story of the day, though, was Roddick's departure - from the tournament and from tennis. Williams watched his loss to del Potro before taking on Ivanovic in the same stadium Wednesday night.

"He's been the ultimate inspiration for me. Just a great guy, and he did so much for American tennis," Williams said. "I'm really kind of sad."

Roddick chose to walk away after a series of injuries, particularly to his shoulder, made it too tough to remain in the game's upper echelon. A member of the top 10 at the end of nine consecutive seasons, he slid to No. 34 in March, his lowest ranking since 2001. A hurt right hamstring forced Roddick to retire during his second-round match at the Australian Open in January, and he lost in the first round at the French Open and third round at Wimbledon.

Roddick told the world the U.S. Open would be the end of the road a day his second-round match. He wound up winning that one, and a third-rounder, too, riding a wave of support from spectators.

But those two opponents were ranked 43rd and 59th, and the seventh-seeded del Potro provided a far more daunting challenge - especially once he lifted his energy level and got his big, flat forehand cranked up.

The last set won by Roddick was the first of his match against del Potro. After Tuesday night's suspension, they resumed with Roddick ahead 1-0 in the opening tiebreaker, and he needed only four minutes to wrap it up Wednesday, fresh and strong as can be, while del Potro was rather sluggish.

The key was the second set. This time, it was del Potro's turn to control the tiebreaker. Gaining more traction on his opponent's once-all-powerful serve, del Potro whipped a cross-court forehand return right at Roddick's feet on set point.

Del Potro's momentum swing continued when he broke to begin the third set. He hit a drop shot that Roddick chased, grunting loudly, and eventually del Potro deposited a passing winner that left Roddick hanging his head.

Del Potro broke again for a 3-0 edge in that set, producing a drop shot winner that Roddick didn't even chase. As he walked to the sideline for the changeover, Roddick grimaced and flexed his right shoulder - the one that hit a then-record 155 mph serve years ago but isn't what it used to be. He jokingly referred to it as "Hamburger Helper" after his previous match.

When Roddick double-faulted, then missed a forehand, to fall behind 3-2 in the fourth, the competitive portion of the match was essentially done. The rest of the way was a chance for spectators to salute a guy who always wore his emotions on his sleeve while being the best U.S. men's tennis player for about a decade.

"It's been a road of a lot of ups, a lot of downs, a lot of great moments. I've appreciated your support along the way," Roddick told the crowd. "I know I certainly haven't made it easy for you at times, but I really do appreciate it and love you guys with all my heart. Hopefully I'll come back to this place someday and see all of you again."