Cape Town - 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 4 minutes 02.67 seconds, with the South African at 0.17 seconds."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.The 1 500m semi-final will take place on Saturday at 20:35 SA time.