American Jessica Pegula, the No. 6 seed, reached the second week of the US Open without dropping a set, overwhelming Spain's Jessica Bouzas Maneiro 6-3, 6-3 in their first meeting Saturday.
"I thought it was pretty straightforward today. I think I just played some solid tennis," Pegula said. "Didn't have to do too much or anything crazy out there."
Against Pegula, Bouzas Maneiro, who grabbed attention at Wimbledon by eliminating defending champion Marketa Vondrousova in the first round, had 29 unforced errors and only five winners.
Since the start of 2021, Pegula has won 25 matches at the hard-court Slams, trailing only Aryna Sabalenka and Iga Swiatek. She next faces No. 18 seed Diana Shnaider, who earned a straight-sets win over Italy's Sara Errani.
Earlier Saturday, Jasmine Paolini defeated No. 30 seed Yulia Putintseva 6-3, 6-4 en route to the round of 16, becoming the first Italian woman to reach that stage of the New York major since Roberta Vinci in 2016.
The fifth-seeded Paolini, 28, joined Coco Gauff as the only women to reach at least the fourth round at every Grand Slam tournament in 2024.
Paolini had never made it past the second round in 16 appearances at majors entering this season. But she reached the fourth round at the Australian Open in January before being the runner-up at both the French Open in June and Wimbledon in July.
"This year has been amazing. ... It's something that's crazy -- if they told me at the beginning of the year before the Australian Open," Paolini said. "This is I think what I was dreaming of, to play at this level with this consistency in these kind of tournaments, stadiums with a lot of people. It's really nice to be in this position."
Since the Open era began in 1968, only two other women have made their first four major round-of-16 appearances in the same year: Christina Sandberg (1970) and Eugenie Bouchard (2014).
Paolini, whose 18 match wins at Slams rank first among women this season, compiled 13 of her 22 winners off the forehand side against Putintseva at Louis Armstrong Stadium and will meet 2023 French Open finalist Karolina Muchova on Monday for a berth in the quarterfinals at Flushing Meadows.
"I'm a fan of her," Paolini said. "She's playing unbelievable. I really love how she plays. She can play every shot, slice, volleys, serve-and-volleys. She's a very complete player, I think, very tough opponent."
Muchova is back in the fourth round at a Grand Slam tournament for the first time since having surgery on her right wrist, doing so by beating Anastasia Potapova 6-4, 6-2.
Muchova made it to the semifinals at Flushing Meadows in 2023 before losing to Gauff. But Muchova didn't play again last season and had a wrist operation in October, returning to the tour in June.
"I'm trying every day to put some work in and get back to where I was -- maybe even better," Muchova said.
She defeated four-time Slam champion and former No. 1 Naomi Osaka on Thursday and has won all three of her matches this week in straight sets.
"To save some energy is always nice. ... Couldn't be better so far," said Muchova, who has been ranked as high as No. 8 and is currently No. 52. "Last year was amazing. I'm trying to follow up."
Against the 38th-ranked Potapova on Grandstand, Muchova displayed the same varied game that worked so well against Osaka. There were 8 aces, 24 winners and just 11 unforced errors. She saved both break points she faced.
In other women's singles results from Saturday, former Australian Open winner Caroline Wozniacki beat Jessika Ponchet 6-3, 6-2, and No. 16 seed Liudmila Samsonova eased past American Ashlyn Krueger 6-1, 6-1.
In the late match, Beatriz Haddad Maia beat Anna Kalinskaya in straight sets. Haddad Maia next faces Wozniacki.
ESPN Stats & Information, The Associated Press and Reuters contributed to this report.