Although it can be dangerous to read too much into heat times, Bolt’s world record of 9.72 looks in serious danger in Saturday’s final and though Asafa Powell and Tyson Gay also eased through, the rangy Jamaican 21-year-old looks unstoppable.

“I just ran the first 50 meters then I looked around to make sure I was safe and I shut it off,” said Bolt, whose odds of becoming the first man since Carl Lewis in 1984 to do the Olympic sprint double have shortened considerably.

Gay, whose morning heat was his first race since he pulled a hamstring five weeks ago, had to work far harder for his 10.09 behind heat winner Richard Thompson of Trinidad and Tobago.

Powell ran the fourth-quickest time in 10.02 to advance with seven other Caribbean athletes.

(Additional reporting by Gene Cherry; Editing by Ed Osmond)

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.

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.”

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. (Editing by Ed Osmond)