Bolt and Dibaba light up the track

BEIJING (Reuters) - Usain Bolt delivered a stunning demonstration of his sprinting talent when he clocked 9.92 seconds to reach the Olympic 100 meters semi-finals while barely breaking sweat on Friday.

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.

The first track gold went to Tirunesh Dibaba after the Ethiopian produced a devastating last 300 meters to outkick former compatriot Elvan Abeylegesse, now racing for Turkey, and secure the first part of her targeted long-distance double.

The men's shot was the night's other medal event and it produced a surprise winner with Poland's Tomasz Majewski throwing 21.51 meters to beat his pre-Games best by more than half a meter.

There was no doubt, however, about the highlight of a balmy night in the packed 91,000 Bird's Nest.

"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.

Any fears about local conditions having a detrimental effect on the distance runners were blown away as Dibaba and Abeylegesse shattered their best times to join Wang Junxia, who set the world record 15 years ago, as the only women to break 30 minutes.

Dibaba played a patient game but let rip to finish in 29 minutes 54.66 seconds to Abeylegesse's 29.56.34. American Shalane Flanagan took bronze in 30.22.22.

"I have repeatedly won gold medals in the world championships but that was nothing for me," Dibaba said.

U.S. DENIED

The United States went into the shot with real hopes of a clean sweep but had to settle for just a silver for Christian Cantwell (21.09) with Andrei Mikhnevich of Belarus third on 21.05.

Adam Nelson, silver medalist in the past two Olympic Games, failed to register a scoring throw while his world champion compatriot Reese Hoffa finished seventh.

But it was better news for America in the heptathlon where Hyleas Fountain had a great day.

Fountain enjoyed ended 64 points ahead of Nataliia Dobrynska of Ukraine with Briton Kelly Sotherton in third.

The event concludes on Saturday with the long jump, javelin and 800 meters.

Bernard Lagat, trying to win 1,500 meters gold for United States after taking silver and bronze for Kenya, made hard work of his heat, finishing fourth but reaching the semi-finals.

At least he made it, unlike Athens 400 meters hurdles champion Felix Sanchez of the Dominican Republic who rounded off a miserable season by failing to advance from the first round.

There was disappointment too for Sweden's Carolina Kluft, who opted not to defend her heptathlon title but failed qualify for the triple jump final.

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