British number one Kyle Edmund made a first-round exit from the US Open for a second successive year after losing a five-set marathon to Pablo Andujar.
Edmund fought back from behind to take a fluctuating match into a decider.
But his game deserted him in the final set as Spaniard Andujar won 3-6 7-6 (7-1) 7-5 5-7 6-2 in four hours 21 minutes - the longest match at this year's tournament so far.
Johanna Konta and Dan Evans are now the only Britons left in the singles.
Edmund has not progressed past the third round at a Grand Slam since reaching the Australian Open semi-finals in 2017, losing in the first round in three of the past five majors.
"I'm still enjoying my tennis, absolutely," he said.
"It's a great sport - you work on your physical condition, mental, tactical, so many avenues to get better at. It is exciting.
"I've been training very well and putting in the effort, of course you love to see results from that but tennis doesn't work like that."
Edmund, the 30th seed, led by a set and a break against 33-year-old Andujar before his grip on the match was loosened by an increasing number of unforced errors.
The 24-year-old Yorkshireman steadied his game - built around that explosive forehand - to take a fourth set, where 25 winners outnumbered 11 mistakes off his racquet.
Edmund had only taken four of 12 break points in the match before finally finding a ruthless edge when he needed to most.
On Andujar's serve at 6-5 in the fourth, Edmund walloped three winners to tee up three break points and forced a decider at the first opportunity with another precise backhand which left his opponent wafting.
But all that hard work was undone by a poor final set where fatigue in warm New York conditions, albeit nowhere near as hot and humid as last year, may have contributed.
Initially it looked as though Edmund would go on to win after he broke in the second game, only for the Briton's game to quickly unravel.
After Andujar immediately broke back, Edmund missed three more break points in the fourth and was eventually outfought in a fifth game where he had saved four break points.
Andujar, never ranked inside the world's top 30, powered an ace down the middle to set up two match points, needing just the first when Edmund's frustrations were summed up by a framed backhand which flew off court.
"Obviously I feel disappointment losing like that, you want to be rewarded for your efforts," said Edmund, who has suffered endurance problems and struggled with a knee injury in the past two years.
"I think I'm in a better place than I was a few months ago, I'm playing better and competing better throughout the match.
"But being a break up in the fifth, getting broke back and then 0-40 - it is small margins and I'd love to take advantage of those opportunities."
Analysis
BBC tennis correspondent Russell Fuller
Kyle Edmund's thoroughly dispiriting Grand Slam year came to an end after four hours and 21 minutes of hard toil on court 13.
He has failed to advance beyond the second round of a major in 2019. Knee problems held him back in both Melbourne and Paris; physical issues at Wimbledon; and here in New York he was not quite able to put all the pieces of the jigsaw back together.
It was alarming to see him lose the last six games of the match, but it was only Edmund's 29th tour-level appearance of the year.
He needs matches, and will play five tournaments in six weeks when the tour resumes after the US Open. That should in turn boost his fitness, form and decision-making.