The event is wide open with a host of leading contenders absent. Olympic champion Marion Jones failed to qualify at the U.S. trials and the first two finishers at last year's world championships, Americans Kelli White and Torri Edwards, are banned for doping.

Greek Katerina Thanou, the Olympic silver medallist in 2000, is also absent after withdrawing in the wake of the scandal over her and compatriot Costas Kenteris's missed dope test which has rocked the Athens Games. U.S. champion Colander clocked 11.31 seconds in winning her heat, with 37-year-old Devers, seeking a third Olympic 100m gold, a comfortable third in her heat in 11.29. Williams won her heat in 11.16.

"It felt great, it was wonderful, it's positioned me well going into the second round, I'm very excited," Colander told reporters.

Former Jamaican Merlene Ottey, taking part in her seventh Olympics at the age of 44 and now representing Slovenia, ran an impressive 11.14 to finish second in her heat. "I feel fantastic," she said.

Belarus's Yuliya Nesterenko clocked the quickest time of the morning with 10.94, a national record, to finish ahead of Ottey, with the first three qualifying in each heat plus the eight fastest losers.

Of the other main contenders Ukrainian Zhanna Block, Frenchwoman Christine Arron and Bulgarian Ivet Lalova, who has the world's fastest time of 10.77 this year, eased through.

Jamaican trio Veronica Campbell, Aleen Bailey and Sherone Simpson also qualified for the next round later on Friday.