"I'll make this short and sweet: I've decided that this is going to be my last tournament," said Roddick, wearing a black T-shirt and baseball cap with his clothing sponsor's logos.
"I just feel like it's time. I don't know that I'm healthy enough or committed enough to go another year," he said. "I've always wanted to, in a perfect world, finish at this event."
The 20th-seeded Roddick is scheduled to play 19-year-old Bernard Tomic of Australia in the second round Friday night at Arthur Ashe Stadium.
"I think I wanted an opportunity to say goodbye to people, as well. I don't know how tomorrow's going to go, and I hope it goes well, and I'm sticking around," Roddick said.
He was, by turns, in reflective and joking moods while speaking to reporters about his decision.
"If I do run into some emotions tomorrow or in four days, I don't want people to think I'm a little unstable. Or more unstable," Roddick said with a chuckle. "So that's why I came to this decision."
His title in New York nine years ago was the last time an American man won a Grand Slam singles title, and Roddick spoke wistfully — as he often has in the past — about coming to the U.S. Open with his parents as a present when he turned 8.
He said he's "been thinking about (retirement) for a little bit," and knew for sure that the time now after his 6-3, 6-4, 6-4 first-round victory over 21-year-old American Rhyne Williams on Tuesday.
"I've thought all year that I would know when I got to this tournament," he said, "and when I played the first round, I knew."
In addition to winning his U.S. Open trophy, Roddick also played in four other Grand Slam finals — three at Wimbledon and one at the U.S. Open, losing to 17-time major champion Roger Federer each time. That included a 16-14 defeat in the fifth set at the All England Club in 2009, when Roddick was saluted by spectators who chanted his name at the end of the match.
Buoyed by a booming serve — he used to hold the record of 155 mph — and big forehand, Roddick is 610-212 (a .742 winning percentage) with 32 titles, including two this year at Atlanta and Eastbourne, England. He also helped the United States end a 12-year David Cup drought by winning the 2007 title.
"Look, he's been our best player for many, many years. Do we love to have a guy like that out there? Sure. Was it great that he's American? Sure," said U.S. Tennis Association CEO Gordon Smith. "We could use another dozen Andy Roddicks, and we're grateful for all he's meant to American tennis, to the Davis Cup, to the U.S. Open."
Roddick's announcement came one day after four-time major champion Kim Clijsters played the last singles match of her career, a second-round loss to Laura Robson at Flushing Meadows.
"I haven't done this before. I'm sure it'll be very emotional. I'm sure I'll still be nervous," Roddick said, looking ahead to facing Tomic. "I don't know."
He's been dealing with a series of injuries over the past few seasons, and in February dropped out of the top 20, then 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.
"With the way my body feels, with the way that I'm able to feel like I'm able to compete now, I don't know that it's good enough," Roddick explained. "I don't know that I've ever been someone who's interested in 'existing' on tour. I have a lot of interests and a lot of other things that excite me. I'm looking forward to those."
He mentioned the youth tennis and learning center that his foundation is building in his hometown of Austin, Texas, and a radio show he appears on.
The latter would seem to be a natural second career for Roddick, known for a sharp, often sarcastic, wit. He's never been shy about showing his emotions on the court — whether tossing a racket or insulting a chair umpire or line judge — or sharing his opinions off it.
Roddick grew up in the spotlight and the world watched him morph from a brash, Gen-X kid with plenty of 'tude to something of an elder statesman in the game.
He has spoken out about tennis players perhaps needing a union to fight for their rights the way athletes in U.S. team sports do, and he emerged as a mentor to younger Americans.
Up-and-coming players such as Sam Querrey and Ryan Harrison have thanked Roddick publicly for his help, whether it's offering advice about dealing with life on tour or inviting them to come train with him in Austin.
"I was a little shocked. I think he kept it a very good secret," the 20-year-old Harrison said about Roddick's retirement.
"Honestly, there were a lot of things he taught me, but probably the most important thing on the tennis front was the consistency of every day — every day, working, being out there, putting in time and effort. It's 100 percent. ... If you're going to do it halfway, there's no point in doing it at all. That's what he taught me," Harrison added. "That's what he's done throughout his career and that's what he's all about."
Constantly confronted with questions about why his generation wasn't as successful as previous groups of American men — like Pete Sampras and Andre Agassi in the 1990s, or John McEnroe and Jimmy Connors before that — Roddick did his best to keep adapting his game to try to keep up with Federer, in particular, as well as Rafael Nadal and Novak Djokovic.
He improved his fitness. He added a better backhand. He worked on his volleys.
Eventually, though, he found it too hard to stay at the level he once reached.
"I don't know that I want to disrespect the game by coasting home," Roddick said. "I had plans to play a smaller schedule next year. But the more I thought about it, I think you've either got to be all in or not. That's more kind of the way I've chosen to do things."
Follow Howard Fendrich on Twitter at http://twitter.com/HowardFendrich
AP National Writer Eddie Pells contributed to this report.