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

The former world champion won in 10.03 seconds in a headwind of 1.2 meters per second, ahead of compatriot 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 27 July 27-12 August Olympics were absent.

Asafa Powell was forced to withdraw 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, failing 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 former Olympic champion Liu Xiang qualified for the final but withdrew with a back strain.

Home favourite 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 love this track and this crowd and 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.

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 before the race — won in 53.77 seconds, 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 triumphed in the pole vault.

Christophe Lemaitre shrugged off damp and dismal conditions to win the 200 meters at the London Grand Prix, while Blessing Okagbare upstaged the Olympic and world champions in the women's 100 yesterday.

Lemaitre of France won at the Crystal Palace Diamond League meet in a personal best for the season of 19.91 seconds, ahead of Dutchman Churandy Martina and Marvin Anderson of Jamaica.

Only Jamaicans Usain Bolt and Yohan Blake have gone faster than Lemaitre this season, ahead of the July 27-August 12 Olympics.

"I knew I could run under 20 seconds but to do that here is very good, two weeks before the Olympic Games," Lemaitre said. "Now I'm very confident over this distance. For the Olympic Games, I want to go even faster, because with Bolt, Blake and the other sprinters I think that I must beat my personal best if I want to win a medal."

In the 100, Okagbare of Nigeria won in 11.01 seconds, leaving world champion Carmelita Jeter trailing in second, and Olympic champion Shelly-Ann Fraser-Pryce in last place.

"Whatever you say about the conditions, you have to go out there and do your best," Okagbare said. "That was what I did today and I'm really grateful for that. The time was good. It was a strong field."

Fraser-Pryce said her focus was on the bigger race coming up in the British capital.

"As an athlete you have to take precautionary measures and hope things get better because the Olympics are pretty much on us," the Jamaican said. "I'm working on some things at the moment."

The downpour worsened through the afternoon in south London and — with rain lashing the track — Christine Ohuruogu won the 400 in 50.42 seconds ahead of Amantle Montsho and Rosemarie Whyte.

"I am fit and ready for the Games and looking forward to it," Ohuruogu said.

There were double disappointments for the British public as Olympic fervor mounts.

Olympic silver medalist Phillips Idowu pulled out of the triple jump due to a hip problem, with Christian Taylor of the United States winning with a leap of 17.41 meters.

And Tiffany Porter, who has been carrying a back injury, was in tears after finishing last in the semifinals of the 100 hurdles. Kellie Wells of the United States won the final in 12.57 seconds.