Andy Murray was shocked to be let down by his body in a dramatic first-round victory over Robin Haase at the US Open.
The British number one looked in full control at two sets up against the Dutchman only for cramp to strike suddenly at the start of the third.
Murray's hopes of progressing further appeared very much in peril as he battled to fight through his physical problems.
But battle he did, with a little help from an opponent who was also struggling and blinked within sight of making it two sets all.
Murray reeled off four games in a row from 5-3 down in the fourth to clinch a 6-3 7-6 (8/6) 1-6 7-5 victory after three hours and eight minutes.
The 27-year-old had spoken ahead of the tournament about how he has was in his best physical shape of the year after a tough training camp with his team in Miami.
And what transpired on a hot but not extreme New York day caught him totally by surprise.
"I felt extremely good before the match, and I did train very, very hard to get ready for the tournament," he said.
"For me it was unexpected, and therefore quite difficult mentally to deal with. Sometimes it can happen in one area of your body but when it starts to go everywhere, you don't know exactly where it's going to creep up next.
"When you stretch one muscle, something else then cramps, too. It was tough and very unexpected, especially after an hour and a half.
"So it's unlikely, I would say, that it's down to poor physical condition, because I have trained and played matches. I don't know if it's something I have done in the last few days that's been wrong or not, but I need to try and find out why.
"It's not the worst I have ever felt, but it's the worst I have ever felt after an hour and a half of a tennis match. That's what was worrying about it, is it came after such a short time."
Murray could offer no real explanation of what might have caused the cramp other than to guess it may have something to do with his food and fluid intake.
The match started earlier than expected because of a very quick women's match, and Haase admitted he had had to rush his preparation, but Murray insisted that was not the case for him.
He said: "Sometimes nerves can bring it on. I certainly wasn't nervous at the beginning of the third set after just winning a tough second set.
"I didn't feel incredibly tired or anything. It just happened. The fact that it was the whole body would suggest that maybe it was something to do with my eating or drinking, because if it's through fatigue in one part of your body then that would probably be down to conditioning.
"But cramping in my left forearm? I mean, I didn't use my left forearm a whole lot today compared with other parts of my body."
The silver lining for Murray was certainly that he managed to find a way to win when that looked most unlikely.
Louis Armstrong Stadium has been the scene of many struggles for the Scot, including against Haase in 2011, when he fought back to win from two sets to love down.
Murray said: "I'm happy about that because I could have easily lost that match. I was very close to losing the match. I certainly would not have been the favourite if it had gone to five sets."
Haase was surprised by Murray's sudden decline and knew he had let a golden chance slip away after serving for the fourth set.
The Dutchman said: "He played a few unbelievable returns and that's how the match changed a little bit. At 4-2 I missed two stupid smashes. If I make those, I'll probably lead 5-2 then I'll probably take the set. I was thinking I will win the match."
Haase left the court fuming after being refused the treatment he wanted for a foot problem.
The Dutchman, who is planning to report the issue to tournament officials and the ATP, said: "I have had pain in my foot for two weeks.
"I wanted to get treatment and I didn't get it. I've never heard that before that the physio can deny a treatment or just say, 'I will get the doctor at the next changeover, you will get your pill'.
"We're here at a grand slam. What is that? He said a pill is enough. If I ask for treatment, I should get treatment I think."
Murray next meets German qualifier Matthias Bachinger, who surprisingly beat Radek Stepanek. The match will be played on either Wednesday or Thursday.