NEW YORK -- Five-time major champion Maria Sharapova improved to 23-0 in US Open night matches and returned to the fourth round by beating No. 10 seed Jelena Ostapenko 6-3, 6-2 on Saturday.
"I thrive on playing under the lights for some reason. I love that. I love that challenge," said Sharapova, who won the 2006 title at Flushing Meadows but has been past the fourth round only once since then.
Meanwhile, two-time Wimbledon champion Petra Kvitova, the No. 5 seed, was overpowered by 26th-seeded Aryna Sabalenka of Belarus 7-5, 6-1 in the third round.
Sabalenka, 20, made only 15 errors, 20 fewer than Kvitova, and won 12 of 13 points she served in the second set.
Also losing on Saturday was Wimbledon champion Angelique Kerber, the No. 4 seed. She was eliminated by No. 29 seed Dominika Cibulkova 3-6, 6-3, 6-3.
No. 13 Kiki Bertens was another top seed to lose on Saturday, falling to Marketa Vondrousova 7-6 (4), 2-6, 7-6 (1).
In another match, Madison Keys, who lost in last year's final, rallied to win after dropping the first set to beat Aleksandra Krunic 4-6, 6-1, 6-2.
The 14th-seeded Keys looked out of sorts in the first set, but she was resilient the rest of the way and won 12 of the last 15 games. She said she was nervous -- she even whiffed on an overhead -- but thanked the crowd for pulling her through into the round of 16.
Only No. 3 seed and defending champion Sloane Stephens remains among the top four seeds. After Saturday's matches, 10 of the top 13 seeds are out of the women's draw.
The Associated Press contributed to this report.