Japan’s Naomi Osaka has taken a revenge of sorts on Hsieh Su Wei by beating Hsieh 6-4 6-3 at the Porsche Tennis Grand Prix in Stuttgart, a victory that also ensured Osaka kept the world No.1 ranking.

US and Australian Open champion Osaka prevailed in one hour 24 minutes on first match point to reach the quarter-finals on Thursday after a first-round bye, raising her game after Taiwan’s Hsieh had troubled her early on with a series of winners.

Hsieh had recently beaten Osaka at the Miami Masters after Osaka won their first duel of the year at the Melbourne grand slam. The series now stands at 2-2.

“She is a very tricky opponent. You never know what she will do,” the 21-year-old Osaka said.

Osaka claimed her first Stuttgart victory in a third appearance at the tournament.

Had she lost, Czech Petra Kvitova could have snatched the top ranking from her by winning the title.

Osaka plays Donna Vekic on Friday after the Croation beat Russia’s Daria Kasatkina 6-1 7-5.