Madison Keys, vying to return to the US Open final, was back in the last 16 after a 4-6, 6-1, 6-2 victory over Aleksandra Krunic on Saturday.
"I was definitely a little nervous and she came out playing really well and put a lot of pressure on me from the start," said Keys, whose pre-match aim of getting comfortable on Arthur Ashe Stadium "clearly didn't happen."
"I'm happy to be in the next round," said the 23-year-old American who will face either Wimbledon champion Angelique Kerber or Slovakian Dominika Cibulkova for a place in the quarter-finals.
The match was the curtain raiser to five-time champion Roger Federer's third-round duel with Australian Nick Kyrgios.
The winner of the match will face Australian John Millman, who reached the US Open last 16 for the first time with a 6-4, 4-6, 6-1, 6-3 victory over Kazakhstan's Mikhail Kukushkin.