French Open champion Li Na has failed to progress beyond the first round at Flushing Meadows after losing in straight sets to Simona Halep.
Romanian Halep caused one of the biggest upset in the women's draw so far by defeating the world number six 6-2 7-5 in just over one hour of play.
Halep will now come up against either Mathilde Johansson or Carla Suarez Navarro in the next round on Thursday.
