Top seed Maria Sharapova survived a second-set lapse to advance to a fourth-round meeting with Indian sensation Sania Mirza.
Sharapova was cruising at 4-2 in the second set against Julia Schruff before allowing her German opponent back in.
But the Russian broke again at 5-4 to seal a 6-2 6-4 win.
Mirza earlier reached the last 16 of a Grand Slam for the first time with a 7-6 (7-4) 6-4 win over Marion Bartoli of France.
In a see-saw opening set, Mirza squandered a 4-2 lead and France's Bartoli was hindered by a leg injury.
But Mirza dominated the inevitable tie-break with some powerful strokes to take a one-set lead at Flushing Meadows.
The 18-year-old then made a decisive break in the fifth game of the second set to ease into the last 16.
Mirza's next opponent, Sharapova, said of her own third-round win: "I was moving quite well in the first set and then second set I felt a little sloppy.
"I played a sloppy game at 4-2 serving with the wind, made a few easy errors. But other than that, came back strong."
She is joined in the fourth round by Belgium's Kim Clijsters.
The fourth seed, who has yet to win a Grand Slam, cruised past Japan's Ai Sugiyama 6-1 6-4 and will now face Venezuela's Maria Vento-Kabchi.
Sugiyama, who reached the final of the WTA event in San Diego earlier this month, was outplayed from the start by a rampant Clijsters, who won three hard-court titles in the run-up to the US Open.