World record holder Yuliya Pechonkina won a controversial women's 400m hurdles gold in Helsinki on Saturday.
The Russian was favourite to win her first world crown and she delivered in a world leading time of 52.90 seconds.
But the American team appealed against the result after Pechonkina appeared to have taken her lead leg around the first barrier rather than over it.
But the appeal was rejected, leaving USA's Lashinda Demus and Sandra Glover with bronze and silver respectively.
Demus was second in a personal best 53.27, while her team-mate Sandra Glover, who won world silver in 2003, also ran a pb of 53.32 to take third place.
Pechonkina finished a disappointing eighth at last year's Olympics but said her technique had improved.
"We managed to figure out the peak of my form at the right time," the 27-year-old said.
"The plan was to relax for the first five barriers and then push to the finish."
Demus kept pace with Pechonkina for the first 200m but just failed to stay in touch off the bend.
However, the American was still delighted.
"I keep telling myself it is not gold," she said. "But I'm very satisfied with my time because it is my best yet.
"I just want to be the winner next time."
Australia's defending champion Jana Pittman was not competing in Finland this week because of a stress fracture to her back.