STUTTGART: World number one Naomi Osaka defeated Hsieh Su-wei 6-4, 6-3 in her first clay court match of the season in Stuttgart on Thursday.
US and Australian Open champion Osaka, who lost to Taiwanese veteran Hsieh in Miami last month, secured a place in the quarter-finals against Croatia's Donna Vekic.
Osaka, 21, broke Hsieh three times in total to beat Hsieh for the second time in three attempts this year, having also defeated her on the way to lifting the title in Melbourne.
"She's a really tricky opponent. You never really know what she's going to do," said Osaka.
Osaka needed 84 minutes to dispatch the unconventional Hsieh, a win that ensures she will hold on to top spot for at least another week.
She is less than 200 points ahead of Simona Halep in the WTA rankings, although the Romanian pulled out of this week's tournament with a hip injury.
Top seed Osaka fought off the only two break points she faced, in a lengthy service hold for 2-all in the opening set, before breaking Hsieh in the following game.
That was sufficient to wrap up the first set, and a Hsieh double-fault handed Osaka a break to start the second before she closed out victory with another service break in a performance that featured 22 winners and just 16 unforced errors.
The Japanese star arrived in Stuttgart, where she last played in Stuttgart as a qualifier in 2017, after suffering early exits in her last three tournaments.
"Definitely I've put a lot on pressure on myself and found it hard to deal with in the first few tournaments," said Osaka. "I'm really having fun now though."
Osaka will meet Vekic, a 6-1, 7-5 winner over Daria Kasatkina, for a spot in the last four, while Latvian seventh seed Anastasija Sevastova defeated Germany's Laura Siegemund 6-4, 6-3.