World champion Haruna Asami won the women's 48-kg division and Japanese judoka ended up taking four of Saturday's seven events at the Grand Slam meet in Rio de Janeiro.
Asami defeated home favorite Sarah Menezes in the final.
The other Japanese winners on the opening day of the two-day meet were Kana Abe in the women's 63 kg, Hirofumi Yamamoto in the men's 60 kg and Riki Nakaya in the men's 73 kg.
Hiroyuki Akimoto, another world champion, was eliminated in the quarterfinals of the event won by Nakaya.
Hiroaki Hiraoka and Masashi Ebinuma were knocked out in the semifinals of the men's 60 kg and 66 kg categories, respectively.
This year's world championships will be held in Paris in August.