Reigning world champions Naohisa Takato and Ai Shishime each won their respective divisions on Friday to give Japan an early lead at the Zagreb Grand Prix, a three-day judo tournament in Croatia.
Takato earned a sixth straight win on the International Judo Federation circuit after defeating American Adonis Diaz in the men's 60-kg division at Zagreb Arena.
In the women's 52-kg final, Shishime beat France's Amandine Buchard for her second straight win.
Current men's 66-kg world title holder Hifumi Abe lost to Mongolia's Dovdon Altansukh in the quarterfinals, but rebounded in the repechage for bronze.
Reigning world champ Funa Tonaki and Haruka Funakubo took bronze in the women's 48-kg and 57-kg, respectively.
The world championships will kick off on Sep. 20 in Baku, Azerbaijan, following next month's Budapest Grand Prix.