Semenya won the heat with a time of 1:59.31.
The current world record is 1:53:28 with the Olympic record standing at 1:53:43.
Semenya was the 6th fastest runner in the heats, with Melissa Bishop of Canada clocking 1.58.38 to take the fastest position in the qualifiers.
Many observers insist Semenya, the world No1 this year, will add another gold to South Africa's haul of seven medals - one gold, five silver and a bronze.
The semi-finals are on Thursday (Rio time)‚ which means Semenya – dubbed the “Unlimited Cobra” by her fans‚ would have Friday off ahead of Saturday’s final (Rio time). South Africans can watch the semi-finals on Friday morning and finals on Sunday morning at 2.15am.
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- Caster Semenya: Track record of athlete SA first claimed as a teen wonderEight-hundred-metre track sensation Caster Semenya was celebrated as a golden girl of South African athletics as a junior athlete‚ before riding into a storm of controversy when she was labelled inter-sex.