BERLIN - China's tennis star Zheng Qinwen hit a season-high 23 aces to outplay former world No 1 Naomi Osaka in the first round of the WTA 500 Berlin Open here on Tuesday.

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The world No 8 took 130 minutes to defeat Osaka in three sets, 6-4, 3-6, 6-3, improving her head-to-head record to 2-1.

The victory is Zheng's second of the season over Osaka after beating the Japanese on clay last month at the WTA Italian Open in Rome.

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"I've played against her already on all different surfaces, hard, clay, and now grass court," Zheng said on the court. "She's a tough opponent in the first round. I'm happy that I gave my best today and got my first win at this tournament in three years."

"The last two years, when I came on grass, I was a little bit lost," she added.

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Zheng's 23 aces was the most hit in a WTA Tour-level match this season, besting the previous mark of 19 by Karolina Pliskova against Anna Kalinskaya in Doha.