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).
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.”
Varvara Gracheva produced one of the most stunning comebacks in grand slam history when she came back from 6-1 5-1 down to beat 30th seed Kristina Mladenovic.
The 20-year-old from Russia, playing at her first major championships, saved four match points before taking the second set on a tie-break.
Mladenovic promptly crumbled as Gracheva completed a remarkable 1-6 7-6 (2) 6-0 victory.