NEW YORK -- Serena Williams used a seven-game run midway through the match to grab control and moved into the fourth round of the US Open for the 18th consecutive time with a 6-3, 6-2 victory over Karolina Muchova.
Williams had a bit of shakiness with her serve, double-faulting seven times. Otherwise, she played well, and went from trailing 3-2 at the outset to grabbing the opening set and a 3-0 lead in the second.
Williams is seeking a seventh title at Flushing Meadows and the 24th Grand Slam singles trophy of her career. On Sunday, she will face 22nd-seeded Petra Martic of Croatia for a quarterfinal berth.
In a night match, Madison Keys, the 2017 US Open runner-up, had her blood pressure and pulse checked during a second-set medical visit but held on to beat Sofia Kenin 6-3, 7-5 in an all-American matchup in the third round.
The 10th-seeded Keys saved all eight break points she faced and put together a 26-9 advantage in winners, including 10 aces. She said she was "just not feeling 100%'' against the 20th-seeded Kenin.
Keys made it to the fourth round at Flushing Meadows for the fifth consecutive year. Her next opponent is No. 5 seed Elina Svitolina, who eliminated No. 32 Dayana Yastremska 6-2, 6-0.
Second-seeded Ash Barty advanced to the round of 16 with a 7-5, 6-3 victory over Maria Sakkari.
Barty, the reigning French Open champion who faced tough tests in her first two rounds, employed a steady baseline game and took advantage of 39 unforced errors from the 29th-ranked Sakkari.
This is the second year in a row Barty has advanced to the final 16. She next faces No. 18 Qiang Wang, who beat Fiona Ferro 7-6, 6-3 on Friday.
Third-seeded Karolina Pliskova overcame her emotions and an inspired opponent to advance to the round of 16, downing Ons Jabeur 6-1, 4-6, 6-4.
Pliskova, a former No. 1 who reached the final here in 2016, won despite looking out of sync for much of the match. After Jabeur received treatment on her right knee at the end of the first set and began winning in the second, Pliskova smashed her racket in frustration, earning a warning from the chair umpire.
Pliskova relied on a strong serve game to get back on track. And Jabeur, a Tunisian who had been seeking to become the first Arab woman to reach the fourth round of a Grand Slam tournament, faltered down the stretch. Although she cracked 49 winners, she also had 43 unforced errors, 17 of them in the final set.
In other women's matches Friday, No. 22 Petra Martic upset No. 12 Anastasija Sevastova and No. 16 Johanna Konta knocked off No. 33 Zhang Shuai in straight sets.
Pliskova will take on Konta and Williams will face Martic in the next round.
The Associated Press contributed to this report.