Semenya in Olympic debut 3 years after gender test

South Africa's Caster Semenya leads Mauritius' Annabelle Lascar in a women's 800-meter heat during the athletics in the Olympic Stadium at the 2012 Summer Olympics, London, Wednesday. (AP/Anja Niedringhaus)

Making her Olympic debut three years after being forced to undergo gender tests, Caster Semenya of South Africa finished second in her 800-meter preliminary heat Wednesday.

Semenya was sidelined for nearly a year while track and field's governing body, the IAAF, decided whether to allow her to compete after she won the 2009 world title at age 18. She was tested and eventually cleared to return to action in 2010, then was the runner-up at last year's world championships.

Semenya carried South Africa's flag at the opening ceremonies in London and is a leading medal contender in the 800. She ran her heat Wednesday in 2 minutes, 0.71 seconds, behind the 2:00.47 run by Alysia Johnson Montano of the United States.