South Africa's world champion Caster Semenya produced the fifth fastest 800 metres time in history to win the women's 800m title in grand style this evening - in a new world leading time of 1:55.45.
Semanya, 18, from Polokwane, Limpopo province, possesses an unusually developed muscular frame and a deep voice and is currently at the centre of an inquiry over concerns raised about whether she is male or female.
But she put all the controversy behind her and led the race from the bell to win in a spectacular fashion.
Kenyan world champion and Olympic silver medallist Janeth Jepkosgei was more than 15m adrift for second in 1:57,90, and Jenny Meadows of Britain sneaked into third place on the line, three-hundredths of a second behind Jepkosgei in another personal best.
Nick Davies, a spokesman for the International Association of Athletics Federations (IAAF), confirmed today that the test was requested after Semenya's run last month amid fears she should not be allowed to run as a woman.
"In the case of this athlete, following her breakthrough in the African junior championships, the gossip was starting to build up," said Davies.
Davies described the tests necessary to determine the gender of an athlete as "an extremely complex procedure" involving medics, scientists, gynaecologists and psychologists, the outcome of which is not expected for several weeks. "The situation today is that we do not have any conclusive evidence that she should not be allowed to run," he said.
"It would be wrong today to take a decision to withdraw an athlete. This is a medical condition. It is nothing that she has done. There is a need to make sure rules are followed. We are more concerned for the person and not to make this as something that is humiliating."
The World Championships end on Sunday and Davies was unable to say whether any retrospective action could be taken to strip Semenya of her gold medal were she subsequently to be revealed as male.
"I can't say that if X happens in the future that we will, for example, retroactively strip results. It's legally very complex," said Davies.
"If there's a problem and it turns out that there's been a fraud, that someone has changed sex, then obviously it would be much easier to strip results.
However, if it's a natural thing and the athlete has always thought she's a woman or been a woman, it's not exactly cheating."
Molatelo Malehopo, the general manager of Athletics South Africa, reacted angrily to the rumours. "She is a female," said Malehopo.
"We are completely sure about that and we wouldn't have entered her into the female competition if we had any doubts. We have not been absent-minded, we are very sure of her gender.
"We are aware of the claims that have been made but our aim at the moment is to prepare Caster for the race this evening. We have not started testing and we have no plans to do."
See also: Why the furore over Caster Semenya?