South African runner Caster Semenya has produced a devastating sprint finish to claim the Olympic 800m crown, four years after being denied gold by Russia's Mariya Savinova.

The 25-year-old London 2012 silver medallist turned on the gas with 150 metres to go, crossing the line more than 1.20 seconds clear in one minute and 55.28sec at the Olympic Stadium on Saturday.

Francine Niyonsaba of Burundi took silver in 1:56.49 with Kenya's Margaret Wambui claiming bronze in 1:56.89.

"I used to be a sprinter. I ran the 100m, 200m in high school," Semenya said.

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"It was just a fantastic race. Obviously, there can only be one winner and it turned out good for me. It wasn't about running fast, it was about running a good race."

Semenya has been at the centre of a raging controversy in recent years because of her naturally occurring condition, hyperandrogenism, which causes elevated testosterone levels.

After she won the 2009 world title as a 19-year-old, tests reportedly revealed that she is hyperandrogenous, meaning her body produces an abnormally high amount of testosterone, which makes her more powerful than her rivals.

Rival runners have said they want authorities to revisit rules that limit the amount of testosterone allowed in competitors.

Partially in response to those rumblings, world athletics chiefs implemented restrictions on testosterone levels in 2011.

Following the introduction of those rules, Semenya's times slipped, with many assuming she was taking medication to keep her testosterone levels within acceptable limits.

She was still good enough to take silver behind Savinova in London but the Russian is facing a lifetime ban from the sport after evidence implicating her in doping.

And when the Court of Arbitration for Sport ruled the International Association of Athletics Federations (IAAF) restrictions illegal, Semenya was free to compete in her natural state.

"I just want to be a better athlete. The main focus here was just to run a championship. The coaches told me: just focus on running, nothing else.

"Sport is meant to unite people. I think that's what we need to keep doing."

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Source: Agencies