NAOMI Osaka of Japan reacts after she lost a point during her women’s singles semi-final match against Anastasija Sevastova of Latvia at the China Open tennis tournament in Beijing in this file photo. AFP

TOKYO, Japan — World tennis number one Naomi Osaka split from her coach Sascha Bajin just 17 days after completing back-to-back Grand Slam victories at the Australian Open.

“Hey everyone, I will no longer be working together with Sascha. I thank him for his work and wish him all the best in the future,” the 21-year-old Japanese tweeted in a shock announcement.

Bajin, a former hitting partner to Serena Williams, responded: “Thank you Naomi. I wish you nothing but the best as well. What a ride that was. Thank you for letting me be part of this.”

Osaka, who became the first Asian to hold the top ranking after beating Czech Petra Kvitova in the Melbourne final on 26 January, 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.