For only the Scot will know how he was able to overcome crippling body cramps and a resurgent Dutchman to ensure that his US Open ambitions were not finished by the end of the first day.
Supporters of the 27-year-old are accustomed to being put through the mill at major contests but this encounter with Robin Haase was quite something, even by Murray's dramatic standards.
At two sets ahead and seemingly in control against the world No.70 - and a player who had given the British No.1 an almighty scare on the same court in 2011 - everything seemed to be going quite well.
Granted his serve was not flying off the frame with devastating speed or accuracy, indeed there were five double faults in the first set and nine in all, yet Murray was doing what was asked of him.
Then the problems began. A lot of them. Cramps were tearing through his body and preventing Murray from moving freely. Indeed, at one point during the match he was left quite unable to sit down at the change of ends.
It was reminiscent of the match at the French Open in 2012 when the pain in his back forced Murray to serve underarm against Jarkko Nieminen. Back then in Paris, Murray somehow recovered to win against all the odds. The same pretty much happened here.
Fortunately for the world No.9, a foot problem was hampering Haase, although a final scoreline of 6-3, 7-6 (8/6), 1-6, 7-5 barely told the story of an incredible survival act Murray was able to pull off on the court. He will play Matthias Bachinger tomorrow after the 235th-ranked German upset Radek Stepanek.
Murray was understandably downbeat afterwards having dragged his aching body through Flushing Meadows to fulfil his media obligations. "There's nothing I can do. This is the shape I'm in for the tournament. I feel, or I felt, extremely good before the match, and I did train very, very hard to get ready for the tournament," said Murray, who faces a tough draw.
"For me [the cramps] were unexpected and, therefore, quite difficult mentally to deal with, because, like I say, sometimes it can happen one area of your body. But when it starts to kind of go everywhere, you don't know exactly where it's going to creep up next."
Murray had stressed in the build-up to the US Open how the fitness worries which have proved to be a constant hindrance to his chances of establishing himself among the tennis elite were now a thing of the past. Yet here we were in the third set, Murray barely able to move and looking to have all the dynamism of an 80-year-old walking his dog.
He was, perhaps literally, at pains to describe what had happened afterwards. "When you stretch one muscle, something else then cramps, too. It was tough," he added. "Yeah, like I say, very unexpected, as well, especially after an hour and a half or an hour and 40 minutes.
"So it's unlikely that it's down to poor physical condition, because I have trained and played matches. Like [the match] in Toronto against Tsonga was longer than that and I felt absolutely fine at the end.
"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 necessarily, 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, it came after such a short time.
"I don't think I felt like that after hour and 30, hour and 40 minutes on a tennis court before. I mean, I played four-and-a-half, five-hour matches and felt pretty awful afterwards. But not after an hour and a half."
Certainly everything had gone so well for Murray, around an hour and 30 minutes earlier. He raced ahead 4-0 in the first set and, although Haase began to find his feet, the Dutchman fluffed a chance in the tie-break and allowed Murray to move even further ahead.
His progress appeared serene. Or so it seemed. All of a sudden the 27-year-old could barely walk let alone run under the blazing New York sun. His arms were cramping and his right leg seemed to give him a good deal of pain. Throwing the ball up to serve was horrendously difficult for the Scot. There was pain was etched all over his face.
Haase was up 6-1 in a flash. Murray contrived to lose eight games on the spin and Haase was 3-0 up in the fourth and in the box seat. However, a foot injury continued to upset the world No.70 and he continued to miss opportunities at alarming regularity. There were plenty of those, too.
Despite his discomfort, Haase should still have taken the match to a fourth set, having gone 3-0 ahead in the third. Yet Murray not only got back on serve but, after saving break points, was presented with a serve for the victory, a result sealed when Haase again fluffed his lines.
There was relief for Murray. The future remains to be seen. "It's not the first time it's happened," said the world No.9, grimacing. "I'm sure all of the tennis players have experienced it at some stage. But it was just weird that it happened [when it did]. Because, I mean, even if I was in bad shape I would still be fine normally after that amount of time."
Bachinger, Murray's second-round opponent, is ranked No.235 in the world and spends most of his time on clay. He would have watched this match with some interest, and much more incredulity, just like everyone else did.