Katie Boulter will drop outside the world’s top 50 after losing to Marta Kostyuk in the opening round of the US Open.

The former British number one has had a difficult season and admitted ahead of the contest that she had begun to feel burnt out after heading straight from Wimbledon to the United States.

This was a tough draw against the 27th seed and Boulter was unable to prevent a first opening-round loss here in four years, losing out 6-4 6-4.

Boulter’s only previous match against Ukrainian Kostyuk came in San Diego last spring and brought her the biggest title of her career.

But she was unable to defend her crown because of injury and wins have been hard to come by since, aside from an impressive first title on clay, albeit below main tour level, just ahead of the French Open.

This was a close contest but ultimately it was Kostyuk who took more of her chances, with Boulter converting only two of her 10 break points.

Three of these came in the final game after Boulter, who hit eight double faults, had dug in to save five match points on her own serve, but she could not push the match to a decider.

It is a rare first-round defeat at a grand slam for the 29-year-old, who had reached the second round in nine of her 10 previous appearances in the main draws at majors.