Cuban judoka Idalys Ortiz won Olympic gold in the women's +78 kilogram category on Friday.
Ortiz was awarded the victory over Mika Sugimoto from Japan by a unanimous judges' decision after the golden score period remained scoreless.
It is the second Olympic medal for Ortiz, who won bronze in 2008 in Beijing.
"I knew that I'd done well, but no one's invincible," she said.
For Japan, the result capped the country's worst-ever showing in Olympic judo.
"I don't know why this week's performance has been like this. I was quite confident that we had practised more than any other judo players so I really don't know why we haven't done as well as we were expected to," Sugimoto said.
"I wanted to get a medal for those who couldn't get a medal. But I ended up coming second."
Karina Bryant of Britain and China's Tong Wen won Olympic bronze in the women's +78 kilogram category on Friday.
Bryant, 33, a four-time European champion, took her first Olympic medal by beating the Ukrainian Iryna Kindzerska by ippon in a close fight.
"The crowd spurred me on. It's really nice to share this experience with the British crowd," Bryant said.
Tong beat Maria Suelen Altheman of Brazil by ippon.