Osaka, who became the first Asian to hold the top ranking after beating Czech Petra Kvitova in the Melbourne final on January 26, had worked with the German for just over a year. No reason was given for the surprise decision to part ways, but Japanese media cited Osaka's management company IMG in reporting that there had been a breakdown in the player's relationship with the coach since the start of the year.
According to Japan's Nikkan Sports, some practice sessions with Bajin at the Australian Open lasted just 10 minutes and she sometimes hit without him being present. Osaka, who is scheduled to compete in Dubai next week, began sounding out potential replacements late last year, local media reported.
The Japanese player captured her first Grand Slam crown by stunning Williams at last year's US Open in a final remembered as much for the American's astonishing rant at the chair umpire following a coaching violation. Based in the United States, Osaka linked up with Bajin in late 2017 and enjoyed a breakthrough year, shooting from 72 in the world to the top of the women's rankings.