World record holder Usain Bolt [Images] barely broke sweat despite the sweltering temperatures to cruise through the Olympic [Images] 100 metres heats along with compatriot Asafa Powell [Images] and world champion Tyson Gay [Images] on Friday.

The 21-year-old Jamaican, aiming to become the first man for 24 years to do the Olympic sprint double, started slowly but soon got into his huge loping stride and crossed the line in 10.20 seconds.

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Powell, the former record holder, comfortably qualified for the quarter-finals in 10.16, the third best time of the morning, despite suffering from stomach ache.

"It felt good," the 25-year-old told reporters. "My stomach felt bad after breakfast."

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American Gay had the closest race but looked untroubled by the hamstring injury he suffered at the U.S. trials last month and won his heat in 10.22.

"It (my hamstring) feels good," he said. "I felt a little sluggish in the first round but my body has woke up now."

WORLD MARK

Bolt slowed towards the end but still easily won his heat and, even if his time was well outside the 9.72 he ran to take Powell's world mark in May, he clearly had plenty in reserve.

Powell cantered through the first 80 metres of his heat before slowing almost to a jog and allowing former world champion Kim Collins of St Kitts and Nevis to nearly catch him.

Britain's Tyrone Edgar ran the quickest time of the morning session in 10.13 seconds, two hundredths faster than another Jamaican Michael Frater, who predicted a possible Caribbean sweep in the blue riband sprint.

"There's a very good chance," Frater said. "We're going to have six Caribbeans in the final."

China's best sprinter, the bespectacled Hu Kai, got huge support from a big crowd in the 91,000-seat Bird's Nest but finished fourth in his heat and missed out on qualification.

"I did not start well," he said. "I didn't feel any pressure at all, I felt excited."

With the fastest three men of all time going head-to-head, the 100 metres is one of the most highly-anticipated events of the 10-day athletics competition.

The second round is on Friday evening with the semis and final on Saturday.