They came in apathy... they left in awe. In awe of a Celtic team who, for once this season, as manager Martin O'Neill opined, were 'a credit to the football club.'
The Scottish champions' stirring second-half 3-2 comeback Europa League victory over Turkish side Besiktas gave O'Neill's side only their fourth win in 11 competitive matches.
It's a start. And while one result does not make a season, it might just jolt Celtic out of their recent lethargy.
The triumph has given Celtic a platform upon which to build as the club reignited their Europa League qualification ambitions on Bonfire Night.
Winter may well be coming, but it doesn't necessarily need to be one of discontent among the many malcontents down Parkhead way.
The plaudits have inevitably gone to Camilo Duran and Callum Osmand, the Celtic substitutes who kickstarted the green-and-white revival.
Celtic's own C&C (Camilo and Callum) Music Factory struck all the right chords and notes, made sweet music and had 'Everybody Dancing Now' in the stands as they bagged all three goals.
The lethal Colombian marksman took his personal tally to 13 goals in all competitions as he netted a brace for the second time in a European outing this season.
Read more:
-
The tactical 'freedom' Celtic give Callum Osmand and his unlikely Camilo Duran bond
-
What Martin O'Neill told Kasper Hogh about Celtic goal drought after Besiktas
-
The Celtic 'rollercoaster' Mika Baur is getting used to & how he spends his days off
However, nobody typified Celtic's fighting spirit more than German midfielder Mika Baur, who earned fulsome praise for his performance from O'Neill.
The Irishman waxed lyrical as he said: "Wee Mika Baur was magnificent for us in the middle of the pitch."
He wasn't wrong.
Baur may be small in stature and frame, but he was head and shoulders above everybody else on a night when he came of age in a Celtic jersey on the European stage.
The 22-year-old summer signing from Paderborn moved from being another name on the team sheet to the kind of midfielder Celtic supporters genuinely believe could be something special.
Baur grew into the occasion and then some. He showed the sort of composure, tenacity and willingness to take responsibility that Celtic supporters have come to demand from anyone wearing the famous shirt.
While Baur's display did not necessarily scream superstar, it was one that suggested the player can certainly play football.
It was a night that could prove to be Mika Baur's turning point in his Celtic career.
Baur looked increasingly comfortable against Besiktas as the game developed, helping Celtic find the fight and determination required to turn what looked like being a difficult evening into a memorable one.
He has cut an impressive figure since arriving in Glasgow, and Baur put in the sort of performance that can change perceptions, not just among the supporters but within a dressing room.
When Celtic needed somebody to take responsibility in the middle of the park, someone prepared to put their foot on the ball, take the sting out of the occasion and, crucially, show the courage to demand possession when the pressure was on, Baur did precisely that.
There was something particularly encouraging about his contribution.
After all, German national head coach Jürgen Klopp knows a footballer when he sees one. The former Liverpool manager has already made his admiration for Baur abundantly clear.
Following the midfielder's international breakthrough against Serbia, Klopp described Baur thus: "We've really seen now that he's a wonderful footballer, playing in the toughest league in the world. To hold his own there with his physical attributes and put himself through that, that's truly something special.
"He reminds me of a multiple Champions League winner. Not just visually, but also in his entire disposition."
That is quite an endorsement from a manager who has worked with some of the finest players in European football. Baur's Germany debut was particularly memorable, making him the 1,000th player to represent the country's senior men's national team.
Not bad for someone who was playing his football with Paderborn only recently.
What matters most is that Baur appears to have developed the temperament to handle the extreme demands of playing for Celtic.
There is a difference between looking a decent prospect in the Scottish Premiership and demonstrating that you have the footballing intelligence, temperament and technical ability to cope with European opposition. Besiktas provided a proper examination.
Celtic had to dig themselves out of a hole after falling behind, and the game demanded character. It was Baur who stepped up to that plate and showed plenty of it.
Celtic's Mika Baur before the UEFA Europa League match at Celtic Park. (Image: PA)
The midfielder's energy and willingness to compete were among the features of his display, while one particularly important second-half defensive intervention underlined that he understands there is more to the job than simply looking elegant in possession. He is beginning to look like a player who can give Celtic something different.
It is worth remembering that Baur is still a young footballer learning his trade in a demanding environment. Moving from German football to Glasgow does not simply consist of a change of postcode.
The expectations on Baur are different, the scrutiny is different and the pressure is relentless.
At Celtic, every loss is a crisis and every performance is judged against the expectation of winning. Every misplaced pass can become a talking point, every poor result brings questions and every promising youngster is quickly placed under the microscope.
The Scottish game is unforgiving and also asks different questions of midfielders. There is a physical intensity to it, particularly when opponents decide that the best way to stop Celtic is to turn the middle of the park into a battlefield rather than a football match. Baur has had to adapt to that.
His German football education gives him a useful foundation. What made his display against Besiktas so encouraging was the suggestion that he is beginning to marry those technical qualities with the physical demands of Scottish football. He is not simply trying to play the game the way he played it in Germany. He is learning how to play the Celtic way.
A German education with a Celtic education. Klopp has acknowledged the particular challenge of succeeding in Scotland, pointing to the physical demands of the game and the progress Baur has made since arriving at Celtic.
Scottish football might not always receive the respect it deserves from elsewhere, but nobody who has played in it seriously doubts the demands it places on players. There is no hiding place at Celtic, and Baur appears to be embracing that challenge rather than being overwhelmed by it.
Celtic need players who are prepared to take calculated risks, and Baur looks capable of doing that. There is scope for Baur to become more than simply a supporting act in the engine room.
He can carry the ball, contribute to the attacking phases and, judging by his recent performances, offer a goal threat, too. That versatility is a valuable commodity.
Celtic have had plenty of midfielders who could perform one particular job. Finding one capable of doing several things well is considerably more difficult.
One impressive European performance does not make Baur a superstar, and the history of Celtic is littered with footballers who enjoyed promising beginnings without fulfilling their potential.
Baur now has to demonstrate that he can produce these kinds of performances regularly. That is his next challenge.
The historic German cap, Klopp's glowing endorsement and now a performance against Besiktas that suggests he is beginning to understand what it means to be a Celtic midfielder. It is an impressive collection of milestones for a young man still finding his feet in Glasgow.
Sometimes a breakout performance is about scoring the winning goal. Sometimes it is about producing a moment of individual brilliance.
Sometimes it is about convincing everybody watching that you are ready for a much bigger responsibility. Baur showed that he can handle that responsibility.
There will undoubtedly be tougher examinations ahead. Mika Baur ain't no Franz Beckenbauer yet.
One day that comparison may become rather more than a cheeky piece of Celtic supporters' wordplay.
'Der Kaiser' had a good ring to it. 'Der Bhoy' sounds even better.
Share