Naomi Osaka in shock split with tennis coach Sascha Bajin

World number one Naomi Osaka has split from her coach Sascha Bajin just weeks after winning the Australian Open to complete back-to-back grand slam victories, the Japanese player said on Monday.

"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 tweeted in a shock announcement.

Osaka, who became the first Asian to hold the top ranking after beating Czech Petra Kvitova in the Melbourne final, had worked with the German for just over a year.

No reason was given for the decision to part ways.

The Japanese player captured her first slam by stunning Serena 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.