Caster Semenya of South Africa competes during the women's 800m...

Caster Semenya of South Africa competes during the women's 800m semi finals of the Rio 2016 Olympic Games Athletics, Track and Field events at the Olympic Stadium in Rio de Janeiro, Brazil, 18 August 2016. Credit: EPA / FRANCK ROBICHON

RIO DE JANEIRO — Gold-medal favorite Caster Semenya kept plenty in reserve in the semifinals of the women’s 800 meters and still posted the fastest of the qualifying times in 1 minute, 58.15 seconds.

The South African who was the silver medalist in London four years ago coasted through 500 meters in the middle of the pack before gradually picking up the pace and hitting the front rounding into the final straight.

Semenya has become the unwilling face of the controversial debate in track and field over women with very high levels of testosterone being allowed to compete. She is believed to be one of several female athletes at the Olympics with a condition called hyperandrogenism. The IAAF was last year forced to drop rules that regulated their testosterone levels.

She led the third and fastest heat, with Linsey Sharp of Britain and American Kate Grace advancing as well.

Margaret Wambui of Kenya won the first heat to advance along with Burundi’s Francine Niyonsaba, the world indoor winner.

Joanna Jozwik of Poland won the second heat and advanced along with Canada’s Melissa Bishop, the world championship silver medalist.

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