Brazil's Sarah Menezes took gold in the women's 48kg category on Saturday, defeating reigning Olympic champion Romania's Alina Dumitru.
Dumitru, defending the title she won in Beijing, was outdone by the 22-year-old Brazilian, who gradually took the ascendancy in the final, winning with two scoring throws in the final minute.
Menezes, appearing in her second Olympics, punched her fists in the air and leapt into the arms of her coach.
Dumitru, who said she would retire after the Games, had earlier upset the number one seed and favourite Tomoko Fukumi of Japan.
Fukumi's disappointing day was completed when Hungary's Eva Csernoviczki threw her on the mat to win bronze with an ippon, an automatic winning throw, in extra time.
Csernoviczki had earlier appeared to lose consciousness during a bout with Belgium's Charline van Snick in the quarter-finals, but recovered despite looking a bit shaky.
Third seed Van Snick, 21, took the other bronze defeating Argentina's Paula Pareto, a bronze winner four years ago, in a close fight that also went to extra time.