Tyson Gay insisted he could give Usain Bolt a run for his money at next month's World Championships in Berlin despite his ongoing problems with a groin injury.

Gay, a double world champion, is the fastest man in the world this year at 100 metres and 200m.

But Bolt, the Olympic champion and world record holder over both distances, will be the man to beat in Berlin.

Gay won the 200m at the London Grand Prix at Crystal Palace on Saturday in a time of 20 seconds, 24 hours after Jamaica sprint star Bolt won the 100m at the south London track in a time of 9.91 secs despite running into a stiff head wind.

Asked about defending his 100m and 200m titles in Berlin, the 26-year-old American said: "Right now I'm running on faith and that's more dangerous than anything. When I hear the gun and just run, it's just dangerous."

In May, Gay set the fastest time in the world this year when he ran the 200m in 19.58 secs in New York.

But his fitness problems have cast a cloud over his season in recent times although Gay added: "I'm feeling okay. I've been trying to keep under the radar, trying to get through this groin situation I have but I should be okay.

"My groin has been tight on me, I'm trying to take a painkiller to run through the pain. I've got to be tough about it. I don't feel it when I run, it's after.

"I'm just taking it one day at a time, it's just frustrating. Any time a sprinter feels any type of nagging pain they get frustrated and the mind has to get strong again.

"I didn't get to warm up like I wanted to because of the situation but I don't think about limping once the gun is shot, I just run. The way I slowed down it would definitely have been 19-something (seconds)."

Triple Olympic champion Bolt, who helped Jamaica win the 4x100m in Beijing last year, indicated earlier this week that Gay might struggle to beat him over 100m but the American said: "Of course I don't agree with it, (but) he's supposed to have that type of confidence and right now he has mastered the 100 and I'm still working on it.

"He knows I'm one of the only ones close to either beating him or getting the (world) record. He knows that.

"You could say I shut down 30m out but that's not going to impress him because I'm pretty sure he can do that and run 19 seconds.

"But at the same time I'm not really worried about if he's impressed, if he's not. He's just like me, taking it one day at a time and focusing on the 100m.

"I feel like I haven't proved myself yet until I break the world record. I believe that's what it's all about. Asafa Powell's done it before, he has the potential to do it again, but Usain Bolt right now is the man.

"He deserves all the attention and I like to be under the radar."

There was an American one-two in the women's 1,500m with Anna Willard winning from Shannon Rowbury while the United States filled all the podium places in the men's 400m hurdles with Kerron Clement leading home compatriots Bershawn Jackson and Michael Tinsley.