San Francisco Frontiers - Zheng, Potapova pull off upsets to reach US Open last 16

Keys was followed to the exit by fellow Americans Taylor Fritz and 2025 women's finalist Amanda Anisimova.

Francisco Cerundolo, the 24th seed from Argentina, rallied from two sets down to upset ninth-seeded Fritz 3-6, 4-6, 6-3, 6-4, 6-4 while Austrian Anastasia Potapova beat Anisimova 6-2, 7-5.

Cerundolo next meets big-serving Alexander Blockx, the 28th seed from Belgium who ousted fifth-seeded French Open finalist Flavio Cobolli 6-7 (4/7), 6-3, 6-0, 6-3.

Zheng saved a match point in her 1-6, 7-6 (7/3), 7-5 triumph over Keys, the 2025 Australian Open champion and a US Open finalist back in 2017.

After coming through the second-set tiebreaker, Zheng appeared to be out of steam in the final set.

The former world number four had to come through qualifying after a lengthy recovery from elbow surgery saw her ranking plummet.

Keys raced to a 5-0 lead in the third but Zheng had a last stand in her. She saved match point at 5-1 and just kept rolling, Keys's increasing frustration showing as she banged her head with her racquet after one lost point.

"I just told myself keep holding every single point, never give up, stay there. And somehow little by little it just happened," Zheng said.

Zheng, currently ranked 121st in the world, will face six-time Grand Slam champion Iga Swiatek for a place in the quarter-finals.

She is the first qualifier to reach the US Open women's singles fourth round since Emma Raducanu -- who went on to win the title in 2021.

Zheng who called the months after her elbow surgery "the worst period" of her pro career, was delighted to be in the second week.

"The hard work pays off finally," she said.

Potapova reached the US Open fourth round for the first time, twice recovering a break in the second set to topple 10th-seeded Anisimova.

For Potapova, it is the continuance of a resurgence which has her back inside the top 25 in the world rankings less than six months after she had fallen to 97th.

She next faces fifth-seeded French Open champion Mirra Andreeva, who beat Nikola Bartunkova 6-2, 7-6 (7/5).

- Zverev under the lights -

Poland's Swiatek, seeded eighth as she seeks to cap an erratic season with a second US Open crown, dominated both tiebreakers in a 7-6 (7/3), 7-6 (7/3) victory over 25th-seeded Maria Bouzkova, who broke Swiatek early in each set but couldn't make the lead stand up.

"For sure it was a super tough match," Swiatek said. "It got pretty physical, many long rallies and I had to attack many times because (Bouzkova) was defending really well, getting every ball back."

Men's top seed Alexander Zverev was again due to close out the night session, taking on Chile's Alejandro Tabilo.

In two five-set matches, both spilling into the early hours of the morning, the German has already spent nine hours and 26 minutes on court.

Zverev says he feels fine physically, but he knows he will have to play better if he wants to add a second Grand Slam title to the French Open trophy he captured this year.

Other top players due in action include former women's champions Coco Gauff and Naomi Osaka, along with reigning Australian Open champion Elena Rybakina.

Australian wild card Dane Sweeny, coming off an upset of 13th-seeded Lorenzo Musetti, takes on 21st-seeded Italian Luciano Darderi with a possible showdown with Zverev looming for the winner.

L.Nguyen--SFF