Osaka, Azarenka, Kerber into Stuttgart quarters

World No.1 Naomi Osaka has made a winning start to her clay-court season by beating Taiwan’s Hsieh Su-wei 6-4 6-3 to move into the quarterfinals of the Porsche Tennis Grand Prix in Stuttgart.

World No.5 Angelique Kerber too had little trouble in an all-German battle against wildcard Andrea Petkovic, beating the former top-10 player 6-2 6-4.

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She will play sixth seed Kiki Bertens, who fired 20 aces as she battled back from a set down to beat Belinda Bencic 4-6 6-3 6-4.

And former world No.1 Victoria Azarenka of Belarus stunned fourth seed and defending champion Karolina Pliskova, needing two hours and 13 minutes to battle from a set down to win 4-6 6-3 6-4.

She next takes on Estonian Anett Kontaveit.

Osaka, A two-time grand slam champion who has yet to win a title on clay, found little resistance on Thursday as she avenged her defeat to Hsieh in Miami last month.

“If there is one positive thing I can say about myself, it’s that I learn quickly,” Osaka said.

“So, for me it has been fun because I like to apply what I did wrong in the past, and I think that is what I was able to do today.”

A break was enough for Osaka to win the first set as she looked somewhat uncomfortable on Stuttgart’s quick indoor clay, designed to be similar to next month’s French Open courts.

There was nothing wrong with her serve, however, as she fired seven aces during the contest.

After going 2-0 up in the second set, Osaka grew in confidence and broke again to seal her first win on clay this season on her first match point.

Victory also meant she will hold on to her world No.1 ranking after this week.

Osaka will next face Croatia’s Donna Vekic, who beat Daria Kasatkina 6-1 7-5.

Also advancing to the last eight on Thursday was Anastasija Sevastova, who beat German wildcard Laura Siegemund – the Stuttgart champion in 2017 – in straight sets.

Sevastova and the other six winners on Thursday joined third seed Petra Kvitova in the quarters; a day earlier, Kvitova beat qualifier Greet Minnen for the loss of just five games.