So when he said he'd been tossing and turning over how to finish off Philipp Kohlschreiber at the French Open, everyone believed him.
Having come off at 7-7 in the final set the previous evening struggling with cramp, Murray held firm, saving a break point at 9-9 and finally clinching victory with a big backhand return to win 3-6, 6-3, 6-3, 4-6, 12-10.
The final point was greeted with two clenched fists and an enormous roar, evidence if anyone doubted it as to how much the win meant.
And on a day when Roger Federer was upset by Ernests Gulbis and Novak Djokovic was at his brutal best in crushing Jo-Wilfried Tsonga, the fact that Murray survived at all was something to be grateful for.
As he contemplated today's fourth-round meeting with Fernando Verdasco, the man he beat from two sets down in the Wimbledon quarter-finals last summer, the Scot explained that he had had only five hours' sleep as he replayed the match, to that point, through his mind.
"When you know you have to come back and it's 7-7 the next day and every single point counts, basically you need to get off to a big start," he said. "You're obviously going to be a bit anxious and a bit nervous when you go to sleep, and when you wake up in the night same thing is going to happen. It wasn't the best night's sleep."
But while Murray knows he is going to have to call on all his mental and physical strength if he is to get past Verdasco, his attention to detail certainly won't be lacking.
"I calculated last night that the ball change was going to be after the first game so I knew I was going to be serving with the oldest balls and he'd be serving with the new ones," Murray said, a slight smile creeping across his face. "When the umpire told us that at the start, [Kohlschreiber] didn't actually know, so he went immediately to change his racket because he was going to play with an older racquet.
"Coming out and serving with the old balls and knowing you're going to return with the new ones, I don't know. It was 50-50 really."
The match was also 50-50 when the pair returned just under 16 hours after walking off court the night before, as darkness crept in.
But Murray was much fresher and looked free of the discomfort that had affected him the previous evening, even if he still clutched at his left leg after a number of points.
The Scot had a match point at 9-8, which was saved by a smash from Kohlschreiber, no small effort having mangled two awful ones already since the restart.
In the next game it was Murray who had to save a break point, with a fine serve, before two forehand winners moved him ahead again.
At 11-10, he sensed his chance and a brilliant backhand set up two match points before some beautiful timing sent an inside-out backhand across the German to finally end the world No.24's resistance.
"I woke up today and actually felt pretty good," Murray said. "Last night I was struggling physically, I was cramping towards the end of the fourth set and for quite a lot of the fifth set.
"Today it was more that there was quite a lot of tension and you were kind of willing and urging the balls to go out, and then they drop in.
"It's just a nervy, tentative kind of 30-40 minutes that you spend on the court. It's not easy and I'm just glad I managed to get through."
Murray knows he will have to recover quickly if he is to beat Verdasco, a man who almost ended his dream of winning Wimbledon last summer before finally wilting in the fifth set of their quarter-final, having led by two sets to love.
Verdasco finished off his match with Richard Gasquet, also held over from the night before, and Murray knows he will need to be focused from the first ball.
"He's the sort of guy who has the firepower to take the play away from you a bit and he can dictate the match because of the way he plays and the amount of power he can generate," Murray said. "I'll need to try to keep the ball away from the dangerous areas of the courts, the places he's most comfortable, and hopefully make it tough for him."
Federer looked understandably down after his 6-7, 7-6, 6-2, 4-6, 6-3 defeat by Ernests Gulbis, the Latvian who last year described the Swiss, and the rest of the top four, as boring.
"When you go deep in a fifth set or in a match, margins are so small on both sides that the fitter guy doesn't necessarily always win or the better player doesn't necessarily win," Federer said. "You just have to create chances, and he did that definitely better in the fifth today than me."
Gulbis described the win that took him to his second French Open quarter-final as the greatest of his career, and even tried to win over a Roland Garros crowd which had been partisan in their backing of his opponent, so much so that some crucial points won by Gulbis were greeted with silence.
Novak Djokovic looked every inch the biggest threat to Rafael Nadal's hopes of a ninth French Open title, crushing Jo-Wilfried Tsonga 6-1, 6-4, 6-1 to set up a quarter-final against Milos Raonic, who cruised past Marcel Granollers of Spain in straight sets.
Tomas Berdych beat John Isner 6-4, 6-4, 6-4 and will now play Gulbis.