Top seed Ash Barty and world number two Naomi Osaka both clinched a place in the Western & Southern Open last 16 with victories on Wednesday.

World number one Barty beat British qualifier Heather Watson 6-4 7-6 (7-3) in an hour, 46 minutes at the WTA 1000 tournament in Cincinnati midweek.

In her first victory since Wimbledon, Barty set up a showdown with defending champion Victoria Azarenka, who ousted Alison Riske 6-2 7-5.

Second seed Osaka, meanwhile, rallied from a set down en route to a 4-6 6-3 6-4 win over Coco Gauff, which means the Japanese star will face Bernarda Pera's conqueror Jil Teichmann.

Osaka serves up a treat

Osaka was beaten by Gauff in their previous meeting at the 2020 Australian Open and was forced to battle hard to avoid another defeat here.

The four-time grand slam champion owed much of her comeback win to keeping her poise, dropping just a single point on serve in the third set as she closed out the win.

"Whenever I play [Gauff], it's definitely always very tough," Osaka said. "I felt like today the match was very serve-reliant, so I'm very happy that my first serve didn't let me down.

"I would have been really happy if I was able to turn things around in the first set, but I'm glad that I was able to do it in the second set. I was more just examining her and trying to stay calm. I felt like the last time I played her in Australia, I was definitely not calm at all. Just trying to keep a level head and figure out like what I could do better during the match."

Andreescu undone again

Bianca Andreescu's difficult 2021 continued as the seventh seed was beaten by Karolina Muchova, who recorded her fourth win over a top-10 player this year thanks to a 6-4 6-2 success.

Andreescu – the 2019 US Open champion – has found it tough since retiring from the final of the Miami Open in April. Having withdrawn from Strasbourg at the quarter-final stage, she lost in the first round at Roland Garros and Wimbledon, winning just one of three matches in between those majors as she recovered from ankle trouble and COVID-19.

Third seed Aryna Sabalenka also crashed out, eliminated 5-7 6-2 7-6 (7-4) by Paula Badosa, and she was joined out the door by fourth seed Elina Svitolina, who lost 7-5 2-6 6-4 to Angelique Kerber.

Olympic gold medallist Belinda Bencic, two-time Wimbledon champion Petra Kvitova, former world number one Garbine Muguruza – the eighth seed – and Elena Rybakina also progressed, claiming straight-sets wins over Veronika Kudermetova, Shelby Rogers, Caroline Garcia and Elise Mertens respectively.

Halep succumbs to injury

Simona Halep's tournament was cut short after the 12th seed withdrew from her third-round match against Jessica Pegula.

Pegula was handed a walkover following a scan which revealed a right adductor tear for three-time Cincinnati runner-up Halep, who is hoping to be ready for the US Open.

"Unfortunately, a scan this morning showed that I have a small tear in my right adductor and therefore it would be too risky for me to play tonight," Halep tweeted. "I will rest up and do everything I can to be ready for the @usopen."