Fourth seed Agnieszka Radwanska became the first major casualty of the US Open when she was dumped out in the second round by Peng Shuai.
Radwanska dropped just one game in a rapid first-round win over Sharon Fichman but world number 39 Peng was a deserved 6-3 6-4 winner.
The Chinese player looked like she might have missed her chance when two match points went begging, one on the Radwanska serve at 5-3 and the second on her own delivery.
Radwanska had a chance to make it 5-5 but missed it and Peng took her third match point with a backhand winner on to the line.
It was deja vu for Radwanska, who suffered her only previous loss to Peng in the second round at Flushing Meadows four years ago.