South African Caster Semenya racked up a season's best as she safely negotiated the first round of the women's 1500m in her audacious bid for a world championships middle-distance double on Friday.
Semenya came in second behind Ethiopia's defending champion Genzebe Dibaba, who won the heat in 4min 02.67sec, with the South African at 0.17sec.
"I am in good condition," said Dibaba. "Last year I had injuries but I am good now.
"The event is very strong with Sifan (Hassan) and Caster, so it will be a very fast race I think."
Semenya is back in the spotlight following a study funded by the IAAF and WADA that showed female athletes with naturally high levels of testosterone enjoy a competitive advantage of up to 4.5 percent over their rivals.
The South African, double defending Olympic 800m champion and also a two-time world gold medallist in the distance, was one of a number of women taking medication to lower her testosterone level until 2015 when the Court of Arbitration for Sport (CAS) suspended an IAAF rule that enforced a limit on naturally occurring levels.
But she has studiously avoided the controversy, instead concentrating on her track performances.
Semenya will be up against it, however, with world record holder Dibaba, Olympic champion Faith Kipyegon of Kenya and the Netherlands' world indoor champion Sifan Hassan, who took bronze two years ago in Beijing, all in top form as the top trio on the world list, all with sub-3:58 clockings.
Kipyegon and Hassan have won two Diamond League meetings each this season -– the former in Shanghai and Eugene and the latter in Rome and Paris -– while Dibaba, who may not be in 3:50.07 world record form of two years ago, has clocked 3:57.82 en route to her 4:16.05 mile victory at the Diamond League meet in Lausanne last month.
Hassan (4:08.89) won the second heat ahead of American Jennifer Simpson, while Kipyegon claimed victory in the third and final heat in 4:03.09.
Whatever the result, hopes will be high that Monday's 1500 final will not be tainted as the Olympic final in the same stadium at the 2012 London Games.
In that race, six of the top nine athletes have been disqualified for doping violations.
Such was the fallout, the International Olympic Committee has yet to publicly confirm any medal re-allocation, with just Bahrain's Maryam Yusuf Jamal listed in bronze medal position.