World number one Iga Swiatek survived a first-set scare to defeat Zheng Qinwen in the last 16 at the Cincinnati Open.

Swiatek, who is the top seed, will face Wimbledon champion and 10th seed Marketa Vondrousova in the quarter-finals.

Czech Vondrousova, 24, beat American Sloane Stephens 7-5 6-3 in their last-16 tie.

American world number three Jessica Pegula, who won the Canadian Open title last week, faces the Czech Republic's Marie Bouzkova in the last 16 on Thursday.

China's Zheng knocked out seven-time major champion Venus Williams in the second round on Wednesday and took a surprise 3-0 lead against Swiatek in windy conditions.

Zheng was broken in the fourth game to hand Swiatek a lifeline but the 20-year-old held her nerve to break the four-time Grand Slam winner again and claim the first set.

However, Swiatek regained her composure quickly - swapping her white outfit for a black one - and breezed through the second two sets in rapid time.

Swiatek said her coach suggested the outfit change a couple of months ago as a way to "reset" and go into the second set "with a different vibe".

She added: "I thought this was a bad [idea] but I tried this time and it worked, so thank you coach."

Meanwhile, Vondrousova converted four of five break points in her win over 30-year-old Stephens.

Earlier, world number four Elena Rybakina - the 2022 Wimbledon champion - retired when leading 6-4 2-5 in her match against Jasmine Paolini, sending the Italian qualifier into the final eight.

Greek eighth seed Maria Sakkari advanced with a 3-6 6-2 6-3 win over Czech Karolina Muchova.

In the other last-16 ties, Linda Noskova of the Czech Republic faces American seventh seed Coco Gauff, Wimbledon finalist Ons Jabeur, who is seeded fifth, takes on Croatia's Donna Vekic and Russian second seed Aryna Sabalenka plays compatriot Daria Kasatkina.