World number one Karolina Pliskova made a stunning comeback to beat China's Shaui Zhang and reach the US Open fourth round.
World number 26 Zhang had match point at 5-4 in the second set, but Pliskova turned it around to break and won the next two games to take it to a decider.
The Czech 25-year-old then fought back from 2-0 down in the third to come through 3-6 7-5 6-4.
The top seed will now face either Jennifer Brady or Monica Niculescu.
Pliskova is one of three players who can top the women's rankings at the end of the tournament, along with Ukrainian fourth seed Elina Svitolina and Wimbledon champion Garbine Muguruza.