Tyson Gay prepared for the anticipated chilly Olympics here by winning the 100 meters at the London Grand Prix in dreary conditions Friday.

The former world champion won in 10.03 seconds in a headwind of 1.2 meters per second, ahead of fellow American Ryan Bailey and Nesta Carter of Jamaica.

"I'm in pretty good shape, I just need to work on some things on my groin area with my physio and I should be good to go," Gay said. "I feel I know how to mentally prepare for this type of weather and this was the best place to prepare for the games."

Gay's main rivals for the July 27-Aug. 12 Olympics were absent.

Asafa Powell withdrew with a groin strain to ensure he is fit for the games, and Olympic champion Usain Bolt sidestepped the event for tax reasons.

There was a lackluster performance from home sprinter Dwain Chambers, who is preparing for the games after a lifetime Olympic doping ban for British offenders was lifted. Chambers failed to even advance from the heats.

In the 110 hurdles, Aries Merritt of the United States won in 12.93 seconds, equaling his own world-leading time this year, after 2004 Olympic champion Liu Xiang qualified for the final but withdrew with a back strain.

Home favorite Mo Farah enjoyed a comfortable victory in the 5,000 meters in 13 minutes, 6.04 seconds, more than 3 seconds ahead of Collis Birmingham of Australia after upping the pace in the final two laps.

"I'm in great shape," Farah said. "It was important to work on my speed a bit. Conditions were not great, but ... I'm looking forward to the Olympics. It's not long to go.

"I just have to think of it as another race and forget it's the Olympics, but I'm quite looking forward to it."

In the women's 5,000, world champion Vivian Cheruiyot led home a Kenyan 1-2-3-4 finish.

World champion Dai Greene was denied victory in the 400 hurdles, finishing second behind Javier Culson just like at the Paris leg of the Diamond League two weeks ago.

It helped Culson acclimatize for the Olympics.

"I'm not used to the weather, in my country it is very tropical," the Puerto Rican said.

There was, however, an unexpected British success in the women's 400 hurdles. Perri Shakes-Drayton, ranked 21st in the event, won in 53.77, more than 1.7 seconds ahead of 2008 Olympic champion Melaine Walker, who was fourth.

European champion Irina Davydova of Russia was second, followed by Kaliese Spencer of Jamaica.

"It gives me confidence knowing that my training is going well," Shakes-Drayton said. "But I'm not going to let it get to me too much."

The long jump was won by Australia's Mitchell Watt, and Bjorn Otto of Germany took the pole vault.