Tyson Gay didn't look like a man preparing to end Usain Bolt's sprinting supremacy at the world championships next month.

Limping and lethargic, Gay won the 200-meter race at the London Grand Prix in 20.00 seconds on Saturday. He then needed painkillers to deal with a groin injury and went straight from the track to a treatment room at the Crystal Palace.

Making the worlds in Berlin will be quite a challenge for Gay. The 26-year-old American remains confident, though, that he can defend his 100 and 200 world titles against Bolt, the Olympic champion and world record-holder.

Gay says he's "taking it one day at a time.

"My groin has been tight on me, I'm trying to take a little Advil to run through the pain. Right now I'm running on faith and that's more dangerous than anything. I don't feel anything when I hear the gun. I just run and I'm dangerous.

"It's after that I feel it."

Meanwhile, Bolt and his teammates ran the fourth-fastest 400-meter relay time in history _ 37.46 seconds. Bolt anchored the team that included fellow Jamaicans Yohan Blake and Mario Forsythe, plus Antigua's Daniel Bailey, representing the Kingston-based Racers Track Club.

In the 200, Gay overtook fellow American Wallace Spearmon on the bend and held a clear lead going into the straight, allowing him to relax in the final 30 meters.

"I didn't get to warm up like I wanted to because of the (injury) situation," Gay said. "The way I slowed down it would definitely have been 19-something."

Gay's motivation to make Berlin is the opportunity to reassert himself in the sport. Bolt established himself as the world's fastest man with a series of astonishing performances at the Beijing Olympics last August, setting world records in the 100 and 200 while also being part of the Jamaica team that broke the world mark in the 400-meter relay.

A year earlier at the 2007 worlds in Osaka, it was Gay recording a clean sweep of those events. The Beijing plans, though, were stymied by a hamstring injury, and there's a sense of history repeating itself for Gay.

"I'm just taking it one day at a time, it's just frustrating. Any time a sprinter feels any type of nagging injury pain they get frustrated and the mind has to get strong again," Gay said. "I haven't been training for a couple of weeks. I've been trying to keep under the radar, mentally I'm just trying to get through this groin situation I have but I should be OK."

Gay has run the fastest 200 in the world this year _ 19.58 in New York in May. Bolt's best this season is a 19.59 this month in Lausanne, Switzerland.

"I think he (Gay) has a lot of time to get over it," Bolt said. "So he should be ready."

The two were to compete in a 400 relay later Saturday, but Gay was advised to rest.

Gay will now go to Stockholm for Friday's DN Galan meet. But first, that troublesome groin will receive medical attention.

"There's not much treatment I can have for it," Gay said. "It's one of those freak accident type of things and bad luck. The doctor said I could have had it for years and running at these type of speeds putting a lot of pressure on my groin, which couldn't take this type of pounding.

"But I'm in the best shape of my life."

In the women's 100, American Carmelita Jeter ran 10.92, lowering her career-best by 0.04.

"It felt really good. It could have been better," the 29-year-old Jeter said. "I'm really excited about Berlin."

Also, double Olympic champion Tirunesh Dibaba of Ethiopia returned to the track to win the women's 5,000 in 14:33.65, fastest in the world this year, and Lashinda Demus posted a world-best time this year in the 400 hurdles _ winning in 53.65, 0.13 quicker than when winning the U.S. title last month.

World champion Kerron Clement led a U.S. podium sweep in the men's 400 hurdles. The 23-year-old Olympic silver medalist clocked 48.85 to head 2005 world champion Bershawn Jackson and Michael Tinsley.

Dwight Phillips of the United States won the long jump with a leap of 27 feet, 4 inches.

Olympic silver medalist Sally McLellan won the 100 hurdles in 12.65, while fellow Australian Steve Hooker took the pole vault at 18-8 1/4.

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AP Sports Writer Graham Dunbar contributed to this report.