He broke his own record, set in May in New York, by .03 second and became the first sprinter to set the world record in an Olympic final since Donovan Bailey ran 9.84 at the 1996 Atlanta Games.
Bolt beat Richard Thompson of Trinidad and Tobago by 0.2 second -- more than a body length -- while American Walter Dix was third.
Asafa Powell, the Jamaican who held the world record for three years before Bolt grabbed it, continued his string of disappointments in big races, fading to fifth for the second straight Olympics.
American Tyson Gay, who was supposed to be the third part of a so-called dream race, was eliminated with a fifth-place finish in his semifinal. Maybe it was a good thing -- now he won't be lumped in that list of seven guys who got blown out by the "World's Fastest Man."
Bolt's specialty has been the 200 meters, which he will be a heavy favorite to win next week in what would be the first men's Olympic sprint double since Carl Lewis in 1988. But Bolt persuaded his coach 13 months ago to let him try the dash -- and what quick progress he has made.
"Usain was spectacular," Powell said. "He was definitely untouchable tonight. He could have gone a lot faster if he had run straight through the line."
Bolt is 6-foot-5, one reason he was never really pegged to run the 100 -- men that tall aren't supposed to be able to get out of the starting blocks and start accelerating fast enough to win the shortest sprint.
Bolt actually skidded from the blocks in this one -- not perfect, but then again, he didn't really need to be. He needed 41 strides to cover the 100 meters and practically loped past the finish line, looking to his right but finding nobody there.
When he crossed, he kept running about halfway around the track. He did a hip-swiveling dance, blew kisses to the crowd, clowned around as if flying, and held up the Jamaican flag. Later, he took off his golden spikes, which will, of course, look great next to his gold medal.
Bolt had always seemed Olympic champion material in the 200 meters, and there was long and spirited debate between him and his coach, Glen Mills, about which other race to make part of his program.
Mills liked the 400, thought Bolt was better built for that. Bolt didn't like that kind of work -- too grueling.
So he committed to working on his starts, so important in these races. After less than a year of training in earnest, he lined up on Randall's Island in New York and routed Gay to set the world record at 9.72 seconds.
Even then, Bolt and Mills played games about whether he would go for the double at the Olympics. They were just messing with everyone. A guy this fast doesn't say no when the chance is there.