Wimbledon champion Petra Kvitova has been knocked out of the first round at Flushing Meadows by Alexandra Dulgheru.
The number five seed has struggled for form since her win at SW19 and fell to straight sets 7-6 [7/3] 6-3 against her Romanian opponent.
World number 49 Dulgheru had only played one singles match since June because of injuries to both knees.
The 22-year-old will now face compatriot Monica Niculescu in the next round.
For Kvitova, she has become the first reigning Wimbledon title holder to exit the US Open in the first round.
