Iga Swiatek of Poland serves to Zheng Qinwen of China (not in photograph) during the Western & Southern Open at Lindner Family Tennis Center on Aug 17, 2023 in Mason, Ohio. (PHOTO / AFP)

Iga Swiatek used an outfit change to help her reset after a poor start and beat China's Zheng Qinwen 3-6 6-1 6-1 on Thursday and set up a Cincinnati Open quarter-final clash with Wimbledon champion Marketa Vondrousova.

Second seed Aryna Sabalenka sailed into the last eight with a tidy 6-3 6-3 win over Russia's Daria Kasatkina but it was the end of the line for world number three Jessica Pegula and number four Elena Rybakina.

Pegula, champion in Canada last week and winner of a Tour best 27 hardcourt matches this season, was dumped out 6-4 6-0 in a rain disrupted contest by Czech Marie Bouzkova, who improved to 4-2 against the American.

Zheng Qinwen of China serves to Iga Swiatek of Poland (not in photograph) during the Western & Southern Open at Lindner Family Tennis Center on Aug 17, 2023 in Mason, Ohio. (PHOTO / AFP)

Last year's Wimbledon champion Rybakina had looked poised for smooth passage, taking the opening set against Italian qualifier Jasmine Paolini 6-4, but retired trailing 2-5 in the second with an unspecified injury.

Iga Swiatek swapped her white outfit for a black one and it led to an instant change in her fortunes as she showed more conviction in her strokes and broke Zheng Qinwen to love three times for a 5-0 lead en route to forcing a decider

Swiatek, who dropped a single game in her previous match at the US Open tune-up event, needed time to work out Zheng but once she did she immediately looked more like the player who has occupied top spot in the world rankings since April 2022.

The Pole looked unsettled as Zheng jumped out to a 3-0 double-break cushion in windy conditions and the Chinese number one refused to let up as she broke for a third time to grab the first set when the Pole sent a forehand long.

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Swiatek swapped her white outfit for a black one and it led to an instant change in her fortunes as she showed more conviction in her strokes and broke Zheng to love three times for a 5-0 lead en route to forcing a decider.

Swiatek motored through the final set and again feasted of Zheng's serve, breaking twice for a 5-0 lead before closing out the contests on her serve when her opponent sent a forehand long.

"Honestly, it's because of my coach," Swiatek said about her outfit change. "He told me a couple months ago that after losing a set it might be a good idea to change your outfit so you can kind of reset and go into the second set in a different vibe.

"I thought this was a bad (idea) but I tried this time and it worked, so thank you coach."

Coco Gauff of the United States returns a shot to Linda Noskova of the Czech Republic during their match at the Western & Southern Open at Lindner Family Tennis Center on Aug 17, 2023 in Mason, Ohio. (PHOTO / AFP)

Awaiting Swiatek in the next round will be Vondrousova, who converted four of five break points during a 7-5 6-3 victory over Sloane Stephens.

In a battle of the teenagers, 19-year-old Coco Gauff claimed a 6-4 6-0 win over 18-year-old Czech Linda Noskova, who failed to hold serve the entire match

Tunisian fifth seed Ons Jabeur also benefited from a retirement when Croatia's Donna Vekic quit while trailing 5-2 in the opening set.

Jabeur, a finalist at last year's US Open, will next face Belarusian Sabalenka in what should a high quality clash for a place in the semi-finals.

In a battle of the teenagers, 19-year-old Coco Gauff claimed a 6-4 6-0 win over 18-year-old Czech Linda Noskova, who failed to hold serve the entire match.

Seventh seed Gauff's win set up a quarter-final meeting with Paolini.

READ MORE: Unseeded Vondrousova stuns Jabeur to win Wimbledon title

Karolina Muchova surprised eighth seed Maria Sakkari 6-3 2-6 6-3 to set up an all Czech showdown against Bouzkova.