Natsumi Tsunoda won the women's 52-kg division on Friday at the Zagreb Grand Prix.
Tsunoda, who claimed gold at last year's Asian Games in Indonesia, beat South Korea's Park Da-sol in the final by scoring a waza-ari on the opening day of the three-day tournament.
Tsunoda, who missed out on a spot at this summer's world championships in Japan, said it was a much-needed victory as she hopes to qualify for the 2020 Tokyo Olympics.
"In order to stay in the race, I need to win every single tournament I compete in. So I'm glad," said Tsunoda, who considers herself trailing world champion Uta Abe and world silver medalist Ai Shishime in the qualification race.
"I was able to concentrate on my opponent and compete calmly."
Among other Japanese judoka, Momo Tamaoki claimed silver in the women's 57-kg division after she was disqualified in her final against Canada's Jessica Klimkait.
The World Judo Championships will take place between Aug. 25 and Sept. 1 at Nippon Budokan, the venue for the 2020 Tokyo Olympics.
