Two days later and we still hadn't worked out whether it was their underdog status, or the ancient pull of the tribe, that had us rooting for Celtic before the night was out.
Since then Scottish football had receded further into the backwaters, dwarfed by the Premier League and irrelevant in Europe, while Celtic themselves remained mired in the sectarian cesspit with their city enemy Rangers.
A plague on both their houses: the game was passing them by, the world was passing them by.
Barcelona on Wednesday night would be everything that the Old Firm were not: artists and peaceniks, spreading the love with their beautiful play, preaching the brotherhood of man through their humility and harmony. When they are passing the ball around it is as if they are passing the universal joint around, inviting everyone to inhale the healing vibes of peace and goodwill. If Lionel Messi were a politician, he would be Gandhi -- the Mahatma Messi.
And now here they were, fetching up in this grim old industrial town with its Balkan hatreds, its primitive football and its appalling food. Barca were bringing their ballet to a bunch of cloggers. They would be kicked up and down the field for their troubles.
Though Celtic were our neighbours, one couldn't in all conscience cheer for them against the good guys, the Gary Coopers, the white knights in an otherwise tawdry world. No, it wouldn't be right, it wouldn't even be moral.
But bedad, right or wrong, it didn't take long to start deviating from the one true path. We found ourselves being lured to the dark side, almost against our will. Barcelona's siege had started early. But with every tackle, with every Celtic clearance, another piece of our resolve crumbled. The longer the home side held out, the stronger the gravitational pull became.
Indeed it had set in before a ball was kicked at all, when both sides walked out to a thunderous roll of noise. And when Victor Wanyama, Celtic's emerging Kenyan star, powered a header home in the 20th minute, all resistance crumbled, like a storm levee washed away in a tidal flood. The roar around Celtic Park was volcanic. "It is no myth," wrote a visiting journalist, Joan Poqui, in Mundo Deportivo, "the stadium, literally, shook."
What's more, the home players didn't resort to kicking and hacking. Their discipline in fact was nigh immaculate. They were defending with rigour and intelligence. In the 12th minute, as Alexis Sanchez jinked past him in the penalty area, Celtic's Nigerian centre back Efe Ambrose was visibly tempted into sticking out a leg. It would have led to an almost certain penalty. But he didn't; he resisted.
It was one of many alarms on the night. Barcelona did what they always do when faced with a stacked defence. They probed and jabbed; they kept the ball moving; they watched and waited. They dragged Celtic's players hither and thither, as if on a string, trying to stretch them sufficiently to engineer a corridor, a channel no wider than a bowling alley, through which they could spear the slicing pass.
They found these openings too, but the home side scrambled superbly all night, getting a body in the way at the moment of maximum danger. When the defence was finally breached, Fraser Forster pulled off the saves, a string of them.
In the 29th, Messi darted into a tiny pool of space inside the penalty area, surrounded by five Celtic players. Andres Iniesta pinged the ball into him. Messi tamed it with merely a dab of his right foot and, in the same movement, turned and let fly with his left. The defenders, though all within touching distance, couldn't get to him. Forster tipped it onto the crossbar with the seams on the fingertips of his gloves.
Celtic, it need hardly be said, never have to be so concentrated in routine matches. Their opponents in Scotland don't demand it of them. They can win without anything near this level of physical effort and mental application. The challenge was in the chasm between what they were used to, week in, week out, and what they were now trying to do. It was like a high jumper suddenly having to jump a foot higher than his previous personal best.
In the first half they were at times struggling to hold on, just poking the ball away in tackles only to find it coming straight back at them again. In the second they showed signs that they were acclimatising, reading the Barcelona ball earlier, making the interception and actually carrying it downfield. This was a team developing and growing on the hoof.
Their manager Neil Lennon rightly received generous recognition afterwards. It was the coaching achievement of his career. One wonders if he, and the club in general, have been liberated by the absence of Rangers from the SPL this season. Instead of being dragged back eternally into that squalid turf war, they could devote themselves to bigger and better things.
With one giant leap on Wednesday they were free of all that insular, pernicious nonsense. It's a forlorn hope perhaps, but one would like to think that for Celtic there will be no going back.