Amusan, who had earlier run an African record of 12.40secs in the heat to qualify for the semi-final outran a quality track which included former record holder USA’s Kendra Harrison to qualify for the final.
“It is a strong feeling. I wanted to get out and go,” she told reporters. “I did what I had to do. Looking forward to the finals.”
She shocked the crowd at Eugene, Oregon, putting on the kind of superb performance usually reserved for prime time in the opening race of the Sunday evening schedule.
Jamaican Britany Anderson won her semi-final in a national record 12.31 seconds, with Puerto Rico’s Jasmine Camacho-Quinn also advancing (12.32).
American Alia Armstrong and Devynne Charlton of the Bahamas also advanced to the final later on Sunday.
“That was a crazy race,” said Britain’s Cindy Sember, who advanced on time. “I have been in shape and I knew it was coming when it matters the most.”
She then stormed to victory in the final becoming the first athlete from Nigeria to win gold at such an event.
The 25-year-old’s 12.06-second performance on Sunday was initially announced as another world record, but was later ruled ineligible as the wind speed exceeded the legal limit.
“The goal was to come out and to win this gold,” said Amusan after winning gold.
“I believe in my abilities, but I was not expecting a world record at these championships. You know, the goal is always just to execute well and get the win. So the world record is a bonus.”