Turns out they were watching impostors. Last night those fans saw the real thing.
The men from the south-west of Ireland may not boast the stellar names of their European glory years, but they brought some old-fashioned Munster virtues to this game. They were stroppy, resilient and ferocious in contact. They lapped up their opponents' errors and they wound down the clock cleverly. They showed a little in attack, a lot more in defence, and they thoroughly deserved the win that brought Glasgow's RaboDirect PRO12 streak to an end.
The result meant Munster inherited Glasgow's place at the top of the PRO12 table. Yet Glasgow can have no real grounds for complaint, for this was an uncharacteristically feeble display in which their big guns failed to fire, they lacked sharpness near the line and they made far too many mistakes for a side with their title aspirations.
"Once Munster get ahead, as they have shown down the years, it is very hard to get back in front," said Gregor Townsend, the head coach. "I thought we looked the better team in the first half, but a couple of mistakes in the second half cost us our lead. Better teams win games, and Munster found a way to do that."
It will not bother Muster one bit that they were booed off the pitch at the end, the Glasgow fans indignant at the time-wasting and cynicism of some of the visitors' play in the closing stages. Glasgow had thrown everything into salvaging something from the game, but still Munster held firm. Victory will have tasted all the sweeter for that scorn.
Indeed, there was bitterness on Munster's side as well, as the actions of some of their players suggested one of them had been bitten late in the game. Rob Penney, the Munster coach, acknowledged that words had been exchanged on the matter, but said he would not comment further until he had more detailed information.
Of course, it was always going to be a physical evening, but the body count had started to mount even before the contest got underway. Paul O'Connell, Munster's Lions lock, and Glasgow winger Tommy Seymour both pulled up during the pre-match preliminaries - rendered hors de warm-up, you might say - with their respective places taken by Billy Holland and Mark Bennett.
It is questionable how disruptive those late adjustments might have been, but there was certainly an edginess about both sides in the first quarter. Not even a second-minute penalty by Duncan Weir, making his first Scotstoun start of the season, could calm Glasgow, as their handling let them down at various points during that period.
That said, their scrum did a pretty good job of redeeming those errors, crushing the Irish side's pack at the first few set-pieces. When Munster caved in yet again in the 24th minute, Weir clipped over his second penalty, restoring the advantage that had disappeared briefly when JJ Hanrahan had opened Munster's scoring with three points of his own four minutes earlier.
Still, though, Glasgow lacked accuracy in their forward efforts. DTH Van der Merwe had managed to get himself across the line, but his score was chalked off for a forward pass, while Byron McGuigan made a hash of gathering the ball when a try beckoned a few minutes later.
Not that Munster did much better - their sporadic forays into the Glasgow 22 usually ending with a turnover or a penalty for the home side. In which light, it would have been almost remiss of the referee not to contribute to the blunder-strewn theme, and Welsh official Ian Davies duly added his tuppence worth by turning up in a red shirt and dark shorts that made him virtually indistinguishable from the red-shirted, dark-shorted men of Munster.
Glasgow's 6-3 lead survived until half-time, but it evaporated soon afterwards when Munster scored a well-executed try in the right corner. It came from a scrum on the other side of the pitch, from where the Munster backs broke swiftly and - at long last - efficiently, as they swept the ball through the midfield. Hanrahan came into the line at pace, and although Glasgow were a little lax, he finished off with the score his running deserved.
With a conversion and a penalty soon afterwards, Hanrahan stretched Munster's lead to 13-6. Soon afterwards, however, they went a man down when a mass brawl in the shadow of their posts brought a yellow card for prop James Cronin, but his departure seemed only to gird the Munster defence as they put in a heroic shift over the next few minutes to keep Glasgow out. They had every right to be proud of their efforts when Cronin trotted back on after his punishment with no damage sustained on the scoreboard.
Still Glasgow poured forward - and still they could not find the killer touch near the line. Even the arrival of Niko Matawalu after 53 minutes could not lift Glasgow's game. The scrum-half ran through his customary repertoire, but he lacked his customary spark. Far from being the cure for Glasgow's problems, he quickly became a symptom of their wider malaise.
So Munster did what Munster always do - they closed out efficiently, soaking up the last of Glasgow's pressure, confident that the game would end with a Glasgow error. Which, as it turned out, is exactly how things did pan out at the finish.