Struggling Heather Watson goes out in first round of US Open

Watson lost the first set 6-2, and though she fought harder in the second she was clearly not fit and ended up on the wrong side of a 6-2 7-5 scoreline.

The British star was up against an opponent who had never won a match at a Grand Slam, and her shotmaking was at times superb.

But whenever she was required to run for a tough ball she seemed unable to move, and appeared to be struggling to breathe freely in between points.

The 24-year-old needed one of the tournament doctors to carry her bags as she gingerly walked from the court after the match.

Watson called a medical time-out at the end of the first set after she doubled over in discomfort on her chair, and was in tears as she was tended to by the doctor.

The Briton appeared to be having trouble with her breathing, and had worked done on her back, but after a long delay was able to return to the court and showed signs of recovering her position in the match.

"She wasn't right physically or mentally," lamented Eurosport analyst Annabel Croft after the match.

Whatever the underlying cause, the result will be a huge disappointment for the 24-year-old, who has now lost in the first round at Flushing Meadows for six years in a row.

For Watson it was her latest setback in New York, where she has now failed to win a main draw match in six attempts, and the continuation of a bad run of form heading into the tournament.

The world 73 won in Monterrey in February, but has since struggled to string wins together and was broken three times in the first set as the threat of an opponent she had never previously met became apparent.