China's Xian Dongmei claimed the women's under-52kg Olympic title when she beat Japan's Yuki Yokosawa.
Xian pinned Yokosawa for ippon to win gold as Cuba's world champion Amarilys Savon took one of the bronze medals.
Belgium's Ilse Heylen beat France's Annabelle Euranie by golden score to claim the other bronze medal.
In the men's 66kg event, Japan's Masato Uchishiba won gold from Slovak Jozef Nrnac. Bulgaria's Georgi Georgiev and Cuban Yordanis Arencibia took bronze.
There were tears and retirement for the veteran Savon, who cost herself a chance of gold when a moment's hesitation late in the semi-final led to last-gasp defeat to Yokasawa.
Savon beat Algeria's Salima Soukri to the bronze and said afterwards: "Finito."
"There was extra pressure on me to get the first medal for Cuba and of course I'm very disappointed to have lost just one second away from the final," said Savon, the bronze medallist in 1992 and 1996.
"But I want to dedicate this medal to my family, my baby daughter Lorena and the people of Cuba."
In the men's 66kg division, Uchishiba's victory was Japan's third gold in four judo events so far, with silver in the other.
But Uchishiba and Krnac's route to the final was made easier when two-time world champion and gold medal favourite Arash Miresmaeili of Iran was disqualified for being overweight for the class.
Miresmaeili was set to meet an Israeli opponent Ehud Vaks in the first round.
Iran does not recognize Israel and bans any contact with the Jewish State.