Former Wimbledon champions Angelique Kerber and Petra Kvitova kept their US Open hopes on track after gritty second-round wins.
Kerber, the 17th seed, is playing in her 50th grand slam at the venue where she made her breakthrough, reaching the semi-final in 2011.
The 2016 Flushing Meadows winner came through a tight all-German clash against Anna-Lena Friedsam 6-4 7-6 (6).
Kerber, 32, who won Wimbledon two years ago, said: "It's always special to return to a place where you won. It's a really special place for me, where it all started in 2011, and I'm still here competing. This is what I love."
Kvitova, the two-time champion at SW19, has never made it further than the quarter-finals in New York.
The 30-year-old Czech, seeded six at this year's championship, was slow to get moving but eventually beat Ukrainian Kateryna Kozlova 7-6 (3) 6-2.
She said: "It was very difficult especially with my nerves, I felt very tight. But it's a grand slam, at the beginning of the tournament it's always like this."