He was even wearing a pair of trousers, as if this was a schoolday and he had just headed to the arena after bunking off.
Traditionalists, though, will be comforted to know that the Scot not only stripped down to shorts and T-shirt but also retained enough of Auld Andy to ensure that this match was an adventure rather than a formality.
Winning top-class contests is a trial for even the best but, for Murray, they regularly appear to be occasions when he is found guilty, sentenced to hard labour but escapes with a facility that suggests he has hidden a file, presumably in those trousers, to saw the bars of a cell.
The world No.3 disposed of Tomas Berdych 3-6, 6-3, 6-4 in two hours eight minutes in London in his first match in Group A of the Barclays ATP World Tour Finals yesterday afternoon. If Murray last defeated the Czech in a gale in the semi-finals of the US Open, then this was far from a breeze. The first set was lost after the Scot failed to convert one of seven break points. Indeed, it took him 11 opportunities to break the Czech's serve.
There was, too, a clear, ominous danger to Murray's hopes of victory in the second set. With the first set lost carelessly because of one poor service game and an inability to convert chances of his own, Murray faced a total of three break points at 1-1. A lost serve then might have led to an irretrievable position but a mixture of strong serving from Murray and a wild forehand from Berdych on a second serve ensured that the Scot held.
This might have a been a shaky foundation but Murray built a victory upon it. He finally broke serve in the next game and the tide turned so much in his favour there should have been a flood warning on the nearby Thames. The first break point was snatched at 1-1 in the third set and Murray strode with some conviction towards an excellent victory against a player who had, until last night, a winning record against him.
Then, just as the crowd was preparing to give rousing acclaim to the returning hero, there was a collective recollection that the US Open champion has of late lost three matches after failing to convert match points.
Thus Murray, who had lost three points on serve in the third set so far, stepped up to clinch the match. At 40-15, he had two points to take the match, to dispose of a troublesome, heavy-hitting opponent who has risen to No.6 and who had forged a 4-3 record over the Scot.
The crowd took a breath and Murray seemed to realise that this was the moment of truth and he did not have a backlog of convincing evidence on which to draw. He could claim with some justification that the break points in this match had been saved by strong play from Berdych. "He completely overwhelmed me," he said of those moments, though a more impartial observer would point to one slack drop shot that gave the Czech a reprieve.
Yet the match points presented a peculiar difficulty. After all, the world No.3 had missed out on two against Milos Raonic in Tokyo, failed to take any of five against Novak Djokovic in Shanghai or one against Jerzy Janowicz in Paris. He had also spent most of the weekend being questioned on these failures.
So the subject was on his mind about 4.30pm yesterday as he had two match points. He then served a double fault, a let, and a fault. Four serves and not one in play. His fifth finally made Berdych play a shot but then the Czech made an unforgivable error by finding the net.
The roar from Murray on converting his second match point raised the roof of the O2 by several inches. "I was thinking the reasons why that had happened," he said of those recent aberrations at the most vital moment. "So, today I focused on every point. I got myself pumped up. I took my time and served it out well."
The Scot has still to receive his trophy from the US Open as it awaits dispatch from New York but he believes winning that title and Olympic gold has given him a strength that stands him in good stead in moments of trial such as the tense shoot-out against Berdych yesterday.
"I've learned a lot this year about how I need to play those big points in big games," he said. That education has been painful of late but Murray used his experience yesterday to stagger over the line in a tight contest.
The crowd rose in acclaim and might have expected a grin of jubilation. Instead, Murray's face contorted into his trademark victory grimace. It may have been the afternoon of New Murray but it was a comfort to many that Auld Torn Face was back.