STUTTGART, Germany -- World No.1 Naomi Osaka of Japan kicked off her clay-court season with a quality win on Thursday, ousting wily veteran Hsieh Su-wei of Chinese Taipei, 6-4, 6-3, to advance to the quarterfinals at the Porsche Tennis Grand Prix.

"I felt like this surface is more suited for me [than for Hsieh] -- and that sounds pretty weird but I think that’s true," Osaka told the press, after her win. "I was sort of in my plan. So, I just felt like I executed what I was trying to do."

Hsieh had given Osaka loads of trouble twice this year already: the Japanese star struggled past Hsieh in three sets en route to her Australian Open title, and Hsieh eventually claimed her first win over Osaka at the Miami Open, which was Osaka’s most recent match.

Photos: Stuttgart sensations: Champions from Petrova to Pliskova

Top seed Osaka, however, executed the best parts of her game in tremendous fashion on the indoor clay court in Stuttgart, taking the victory after one hour and 24 minutes of play, without dropping serve. By virtue of her win over Hsieh, Osaka is assured to hold onto her World No.1 spot for at least another week. 

"If there is one positive thing I can say about myself, it's that I learn quickly," Osaka stated. "So, for me it’s fun because I like to apply what I did wrong in the past, and I think that’s what I was able to do today."

Powerful Osaka had 22 winners to just 16 unforced errors, including seven aces, and converted three of her six break points during the tilt. Hsieh matched Osaka with efficacy on first serve, as they each won 76 percent of points when they got their first deliveries in play. Hsieh, however, was never able to make inroads on the Osaka serve, holding only two break points in the match.

The Japanese star, winner of the last two Grand Slam events, will face Donna Vekic of Croatia in the final eight. Vekic dispatched Russia’s Daria Kasatkina, 6-1, 7-5, earlier on Thursday. Osaka won their only prior meeting in straight sets, in the first round of the Australian Open in 2016. Both Osaka and Vekic were ranked outside of the Top 100 at the time.

"I’ve been fortunate enough to practice with [Vekic] a couple of times and also to play matches against her," said Osaka. "I think the last time we practiced was during grass season, and she’s a really tough person to play against. She has a good serve. There’s not really anything she’s bad at."

Osaka put her stamp on the clash early, saving two break points in an 11-minute service hold for 2-2. The grit required to get through that game paid dividends, as she quickly raced to triple break point against an unnerved Hsieh in the following game. Hsieh saved one break point with a drop volley, but a subsequent forehand miscue handed Osaka the crucial break.

The No.1 seed took that lead and ran with it, blasting consecutive aces in the middle of her service hold for 5-3. Hsieh countered with a dominant service hold at love, to pull within 5-4, but needed to break serve to extend the opening stanza.

Hsieh nearly had her shot when Osaka served for the set, firing a forehand winner to get to 30-30, but Osaka used a strong serve to force an errant return and line up set point, which the Japanese player converted with a winning volley.

Osaka carried her momentum directly into the first set while Hsieh faltered, as the crafty World No.24 from Chinese Taipei dropped serve at love in the opening game, ending with a double fault. Hsieh’s prowess on serve improved greatly by mid-set, but she was never able to recover from her early stumble.

Meanwhile, sturdy serving by the World No.1 got her through tight service games at 2-1 and 4-3, as she maneuvered through the set without facing a break point. Finally, Osaka made another move at 5-3, using an error-forcing forehand to set up match point on Hsieh’s serve. There, a netted error by Hsieh gave Osaka just the tenth main-draw clay-court win of her career.