Kento Momota on Thursday topped the latest Badminton World Federation rankings for men's singles following his runner-up finish at the recent China Open.
The reigning world and Asian champion becomes the first Japanese man to reach No. 1 in the BWF standings in either singles or doubles.
In women's singles, Akane Yamaguchi regained the No. 1 ranking she originally attained in April, when she became the first Japanese player to do so.
In women's doubles, Yuki Fukushima and Sayaka Hirota retained top spot.
Momota, 24, was only restored to the national team in January after serving a suspension for gambling at an illegal casino. Since his return from the suspension, which saw him miss the 2016 Rio de Janeiro Olympics, he has risen quickly up the rankings.
He became the first Japanese man to win a badminton singles world title in August, beating China's Shi Yuqi for the title.
He claimed the Asian title in April with a victory over China's reigning Olympic champion Chen Long in the final.
After entering the China Open as third seed, Momota fell to Indonesia's Anthony Sinisuka Ginting 23-21, 21-19 in Sunday's final.