Beijing - Jamaica seemed assured of their first Olympic gold in the 100 metres race after Usain Bolt and Asafa Powell strolled into the final and US world champion Tyson Gay crashed out at the Beijing Games on Saturday.

Gay, who was returning from a hamstring injury for the Olympic races, went out in the semis by placing only fifth in 10.05 seconds.

"I am pretty upset. I focussed on the Olympics so I am disappointed ... I just didn't have nothing in me today, I ran as fast as I could. I gave it 100 per cent," said Gay.

"The injury was a setback to my training but no excuse because my hamstring feels fine."

The world record holder Bolt clocked a stunning 9.85 seconds even though he eased up after some 70 metres. The former world record holder Powell won the other semi in 9.91 seconds.

Given their personal best times of 9.72 (Bolt) and 9.74 (Powell), only a major mishap could stop them from dominating the decider at 1430 GMT later Saturday and the US not winning a medal at all.

Americans Walter Dix and Darvis Patton, Trinidad and Tobago's Marc Burns and Richard Thompson, Churandy Martina of Dutch Antilles and the third Jamaican, Michael Frater, also made it into the final.

In other action, Kenyan world champion Janeth Jepkosgei and compatriot teenage sensation Pamela Jelimo dominated the 800m semi-finals.

Early Saturday, Russian Valeriy Borchin won the men's 20 kilometres race walk in 1 hour 19 minutes 1 second, holding off three-time reigning world champion and 1996 Olympic gold medallist Jefferson Perez of Ecuador.

Perez trailed by 14 seconds in 1:19:15 hours. Australia's Jared Tallent grabbed bronze in 1:19.42, leaving only fourth place for local hero Wang Hao who turned 19 on the day. The 2004 gold medallist Ivano Brugnetti of Italy had to settle for fifth.

Other finals later Saturday were the women's shot put and the completion of the heptathlon.

In the women's 100m, all the favourites from the US (former world champion Torri Edwards, Lauryn Williams and Muna Lee) and Jamaica (Kerron Stewart, Sherone Simpson, Shelley-Ann Fraser) advanced into the semi-finals.