South Korea's Hwang Kyung Seon defeated Nur Tatar from Turkey to retain her Olympic title in the women's 67 kg division while Argentina's Sebastian Eduardo Crismanich stunned Spaniard Nicolas Garcia Hemme to win a surprise gold in the men's taekwondo 80 kg after hot favourites stumbled Friday.
Beijing gold medalist Hwang, 26, used her greater experience to dominate the 19-year-old Tatar in the final, Xinhua reported.
In the first round, both scored three points simultaneously for a head kick, but Hwang extended her lead to 5-3 by the end of that round.
The 26-year-old went on to score six more points in round two. In the last round, she could play it safe and brought victory home 12-5.
Hwang added a third Olympic medal to her collection and is now the most decorated female athlete in the sport.
Hwang had no trouble advancing to the final, beating German Helena Fromm in the quarterfinals and then dispatching Franka Anic from Slovenia to the bronze medal contest.
Tatar easily cruised into the final as well, with clear defeats over Australian Carmen Marton in her semifinal and American Paige McPherson in the quarterfinals.
McPherson rallied to take bronze against Anic while Fromm beat Marton for the other bronze medal, giving Germany its second Olympic taekwondo medal since 2000.
World champion Sarah Stevenson from host Britain and top seed Seham Elsawalhy of Egypt unexpectedly lost their first bouts. The 2008 Olympic silver medalist Karine Sergerie of Canada was eliminated by Anic at the quarterfinal stage.
In men's 80 kg, top seed Ramin Azizov of Azerbaijan, twice Olympic champion Steven Lopez from the US and the 2011 world champion in the 87 kg, star fighter Yousef Karami of Iran all lost early on, completing the day of upsets.
There was no score in the first two rounds of the final. With 19 seconds to go in the last round, Crismanich finally landed the decisive hit to win 1-0.
Lopez, hampered by an ankle injury, lost in a close match to Azizov in the round of 16 and did not even get to the repechage.