Qualifier Taylor Townsend has continued her remarkable US Open run, with victory over Romanian Sorana Cirstea.
The American world No.116, who stunned Wimbledon champion Simona Halep in round three, beat Cirstea 7-5 6-2.
Townsend is now one match away from a record-equalling quarter-final berth for a qualifier.
"I am here, we are going to ride this thing all the way," she pledged in an oncourt interview. "I will take it as far as I can."
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Townsend next faces fancied Canadian 15th seed Bianca Andreescu, who beat former world No.1 Caroline Wozniacki 6-4 6-4.
"I played great, but so did Caroline," said Andreescu, who won titles this year at Indian Wells and Toronto. "It was super fun.
"Everything is just clicking with me. I have been through a lot."
Germany's Julia Goerges also pulled off a surprise by knocking out seventh seed Kiki Bertens.
Seeded 26, Goerges needed five match points, but eventually got over the line 6-2 6-3.
Also in the last 16 is Elise Mertens, who beat Andrea Petkovic 6-3 6-3 and is yet to drop a set at Flushing Meadows.
Next up for Mertens is American wildcard entry Kristie Ahn, who stunned former French Open champion Jelena Ostapenko 6-3 7-5.
Scheduled for later Sunday (NZ time) is the blockbuster women's fourth-round match between top-ranked title holder Naomi Osaka and American teenage sensation Coco Gauff.
PA
