Caster Semenya won the 800 metres final in a personal best time of 1:55.28 on Saturday, claiming her first Olympic gold medal and using her podium platform to call for unity in sport.
Burundi's Francine Niyonsaba finished in 1:56.49 to claim the silver, her country's second medal in any sport at the Olympics. Kenya's Margaret Wambui won bronze in 1:56.89.
Semenya has dominated the event this season, with three of the fastest four times, but has had to contend with renewed controversies about her gender.
After winning the 2009 world title as a 19-year-old, tests reportedly revealed that she is hyperandrogenous, resulting in her body producing an abnormally high amount of testosterone, which makes her more powerful than her rivals.
An International Association of Athletics Federations (IAAF) rule limiting the amount of naturally occurring functional testosterone for female athletes appeared to have restricted Semenya's prospects but the rule was quashed by the Court of Arbitration for Sport last year.
In Rio, France's Justine Fedronic, who failed to qualify for the 800 final, said she had sympathy for Semenya's situation but did not consider competing against her a fair fight.
"I just want to be a better athlete. The main focus here was just to run a championship," Semenya told reporters. "The coaches told me: just focus on running, nothing else."
"Sport is meant to unite people," she added. "I think that's what we need to keep doing."
The 25-year-old South African won the silver medal in London four years ago. Ahead of the 2016 Games, there was speculation she could break Czech Jarmila Kratochvilova's world record of 1:53.28 set in 1983. It is the longest-standing athletics world record.
"To be honest, we're really not focussed on breaking the world record," she said. "We are focussed more on being the best we can be."
Staying with the pack for the first lap, Semenya let Niyonsaba lead the race up to the 600-metre mark before pulling ahead with an injection of pace to take the gold.
"The race was really quick. The first 400 we were pushing ourselves, it was great," Semenya told reporters.
"It was just about being patient ... I have a very quick last 200, I just have to utilise it."