Iga Swiatek battles her way into the quarters at Cincinnati Masters

Zheng, who beat Venus Williams in the last round, threatened an upset as she opened up a 3-0 lead before taking the first set as Swiatek paid the price for 23 unforced errors.

After taking a bathroom break between sets, during which she also changed her match kit, the French Open champion rallied to force two early breaks against the Chinese 20-year-old and then again in the fifth game.

Although Zheng did finally get a game on the board with a break of her own, it was only delaying the inevitable as Swiatek closed out the set with yet another break.

The decider swiftly went the way of the Pole as she moved 3-0 up before serving out for what was - in the end - a comfortable victory.

"My coach had said to me, 'if you lose the set it might be a good idea to change your outfit, so you can kind of reset and go in the second set with a different vibe' - I tried this time and it worked," Swiatek said during her courtside interview, broadcast by Amazon Prime Video.

Next up, Swiatek faces Wimbledon champion Marketa Vondrousova. The tenth seed had earlier coasted past American Sloane Stephens 7-5 6-3 to reach the last eight and a showdown with the world number one.

Fourth seed Elena Rybakina, though, retired through injury during the second set of her third-round match against Italian qualifier Jasmine Paolini, who progressed with the score at 4-6 5-2.

Karolina Muchova also made it through to the quarter-finals with a hard-fought 6-3 2-6 6-3 victory over number eight seed Maria Sakkari.

READ MORE: Venus Williams upsets World No 16 Veronika Kudermetova in Cincinnati