DOHA (Reuters) - Ugandan Halimah Nakaayi pulled off an upset to win the women’s 800 meters title at the world championships on Monday while favorite Ajee Wilson was left with another bronze as she ran out of steam with 100 meters left.

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Wilson, hoping to become the first American to win the world title over the distance, led for most of the race but was overtaken by Nakaayi down the final straight as the Ugandan won in a national record of one minute 58.04 seconds.

Raevyn Rogers, another American, also sped past to take silver, leaving Wilson with the bronze she also won in London two years ago.

The Khalifa stadium was around half full for the race, providing a much-improved atmosphere compared to Sunday when it was virtually empty.

South Africa’s Caster Semenya, the titleholder and three-times champion, did not take part due to global athletics’ governing body the IAAF’s recently-introduced testosterone regulations.

Rank outsider Nakaayi, who had never before run in a world championship or Olympic final, celebrated by dancing down the track with her compatriot Winnie Nanyondo who finished fourth.

“It the first time that someone from central Uganda makes it to the final. So getting a medal, it means a lot to Uganda. It’s a great achievement for Uganda and even for me,” she told reporters. “It’s my traditional dance from central Uganda.”

OBVIOUS FAVORITE

Wilson had won six of eight races outdoors this season, including claiming the U.S. title -- her 10th overall -- and Diamond League stops in Stockholm, Monaco and Birmingham and Brussels, making her the obvious favorite.

The 25-year-old looked set to continue her dominance as she led from the start.

But, after having to fend off attacks during the first lap, she was unable to repel another from Nakaayi who accelerated past her down the final straight to claim Uganda’s first medal of the championships.

Rogers then came storming out of the blue with a devastating finale to snatch silver.

Semenya lost her appeal at the Court of Arbitration for Sport (CAS) against the rules that mean middle distance female athletes with a high natural level of testosterone must take medication to reduce it.

She then appealed to the Swiss Federal Tribunal which initially allowed her to continue competing while she awaited its final verdict but then reversed that decision after hearing from the IAAF ruling her out of the championships.

The other athletes said her absence did not affect them.

“It’s a little different but it hasn’t directly affected me because there are other great competitors still ahead of me,” said Rogers. “I just focused on the competitors out in front of me.”