Story highlights Tyson Gay wins 100m at the London Diamond League meeting

Home hero Mo Farah sprints away to win the men's 5000m

Aries Merritt takes 110 m hurdles in impressive 12.93 seconds

Liu Xiang of China pulls out before the final with back injury

Tyson Gay tuned up for his Olympic showdown with Jamaican stars Usain Bolt and Yohan Blake with victory over 100m in the Diamond League meeting in London Friday.

In three weeks time just across the British capital, the American will be hoping to cross the line first again in the 100m final, but will be hoping to avoid the damp and cold conditions that all the sprinters faced at Crystal Palace.

The 29-year-old American came surging through to win in 10.03 seconds into a headwind, with Ryan Bailey second and Nesta Carter in third.

Carter's Jamaican teammate Asafa Powell pulled out before the start of the meeting to rest an injury.

"I feel pretty good with the win. The weather wasn't that bad, it's very important to acclimatise and the weather helps me prepare mentally for the Games," said Gay.

"I'm in pretty good shape -- I want that Olympic gold," he added.

Gay is the second fastest man in history behind Bolt, who suffered a surprise double defeat of 100 and 200m in the recent Jamaican trials.

In other action, home hope Mo Farah stormed to victory in the men's 5000m with a blistering final two laps to win in 13 minutes 6.04 seconds.

The 29-year-old is the reigning world champion over that distance but hoping to double up in the 10,000m at the London Games.

He finished clear of Australia's Collis Birmingham and Moses Kipsiro of Uganda.

The men's 110m hurdles was won by American Aries Merritt with a superb season's fastest time of 12.93 seconds in the testing conditions.

Merritt, the winner of the U.S. Olympic trials was set for a showdown with Liu Xiang, who had won his qualifer in impressive style, but the Chinese star pulled out of the final with a bad back.

Puerto Rican Javier Culson beat British world champion Dai Greene in the 400m hurdles, but in the women's equivalent there was home success as Perri Shakes-Drayton stormed to victory in 53.77 seconds, a personal best.

Kenyan star Vivian Cheruiyot underlined her gold medal credentials with a fine win over 5,000m in 14 minutes 48.86 seconds.