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 No. 1 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.
"I need to address the serving," Boulter said. "We've been trying so many different things but nothing is quite working yet. I think that side of my game needs to improve. I think if I can sort that then everything else will fall back into place."
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.
Boulter remains positive about the direction in which she is heading, adding: "You can look at the actual results and you'd probably be like, 'You're having a tough time.'
"I'm actually really excited. I feel like I've got this buzz back again, which I lost a couple of weeks ago in Montreal. I personally would say it was a really pivotal moment in my career. I think that has spring-boarded me off the bottom and taken me back up again."
Kartal exits in dramatic fashion
Sonay Kartal also made a first-round exit and was left looking for answers after being hobbled by cramp in a 6-3, 1-6, 6-1 defeat by 18th seed Beatriz Haddad Maia.
Kartal, who was looking to build on her run to the fourth round of Wimbledon, prides herself on her conditioning and physical fitness but she was cramping so badly in the third set that she was struggling to let go of her racket.
"I've never lost the match from cramp before ever," she said. "We'll look back over everything I ate and drank and see if we can make some changes.
"Last game of the second set I knew I was starting to get a bit of calf (cramp). When just everything is locking out and you're having to peel your thumb off the racket, it's tough. You feel pretty helpless on the court."
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To add to the drama, Haddad Maia also began cramping and, leading 4-0, she could barely roll a serve into the court.
But, cheered on by a band of passionate Brazilian fans that Kartal branded "disrespectful", she found a way to limp across the line.
Kartal was unable to take solace from knowing her opponent was also struggling, saying: "At that point you're in so much pain you go into your little dark place and you just try and get through it. I wasn't thinking about her, I was just thinking, 'I'm going to finish the match'."
Haddad Maia took a long bathroom break after the second set, but Kartal denied that had affected her, adding: "I was happy to get a breather and try to take on as much liquid as I could."
Qualifiers fall
There were also defeats on debut for Fran Jones and Billy Harris, both of whom had to come through qualifying.
Jones rallied after a poor start but lost 6-0, 7-5 to Germany's Eva Lys while Harris, who lost in the final round of qualifying but was given a lucky loser spot, was beaten 6-4, 7-6 (8), 6-4, by 25th seed Felix Auger-Aliassime.
Harris had his chances, particularly in the second set which he led 5-3 before forcing three set points in the tie-break, but he was unable to convert.