Tobi Amusan broke the 100m hurdles world record with a stunning semi-final time of 12.12 seconds - before taking gold at the World Athletics Championships in Eugene, Oregon.
The Nigerian, 25, ran even faster in the final - but her 12.06 was ruled ineligible by an illegal tailwind.
The previous record of 12.20 was set in 2016 by American Kendra Harrison.
Jamaica's Britany Anderson took silver and Puerto Rico's Olympic champion Jasmine Camacho-Quinn got bronze.
Amusan, who had already run a new African record of 12.40 seconds in Saturday's heats, said: "I believe in my abilities but I was not expecting a world record at these championships.
"I wanted to get out and go. I did what I had to do."
Great Britain's Cindy Sember finished fourth in the semi-final won by Amusan, but qualified for the final with a British record of 12.50, beating sister Tiffany Porter's 2014 mark by one hundredth of a second.
It was one of four national records, excluding Amusan's, run in the semi-finals, with another seven athletes equalling or breaking their personal bests.
"That was a crazy race. I actually thought I was running slow. Tobi was amazing, I can't deny," said Sember, who went on to finish fifth in the final.