Joanna Hayes of the United States stamped her authority on a chaotic Olympic 100 metres hurdles competition when she blazed to the gold medal in a Games record of 12.37 seconds on Tuesday.

The light-stepping 27-year-old American ignored a first-barrier pile-up alongside her to scorch over the line in a personal best time that also bettered the 1988 Olympic mark of Bulgaria's Yordanka Donkova by one hundredth of a second.

Olena Krasovska of Ukraine took silver from lane one in 12.45, also a personal best, with 33-year-old American Melissa Morrison repeating her bronze from Sydney in 12.56 -- a time that would have been good enough for gold four years ago.

World champion Perdita Felicien of Canada, the fastest woman in the world this year, crashed to the ground after hitting the first hurdle, bringing down Russian Irina Shevchenko with her.

Felicien had been the pre-race favourite but walked away in tears, flinging her shoes to the ground in anger and frustration.

"The first hurdle came up, I reached for it way too much," she said.

"Before I knew it I was on the ground. I couldn't believe it, there was no coming back. This is going to take four years to sink in."

But even if she had not fallen the burly Canadian, with a lifetime best of 12.46 set this season, may have struggled to stay with Hayes.

The race had been one of the most open finals for years due to the absence of some of the pre-Games favourites.

Gail Devers of the United States, Spain's Glory Alozi and Jamaican duo Brigitte Foster and Delloreen Ennis-London all failed to make the final.

But with the sixth-fastest time in history delivered at exactly the right moment, nobody could deny Hayes was a worthy winner.