We'd already gone through the electrifying preamble, the teams emerging into a sea of colour and a wall of noise that went higher and then higher still.
Just when you thought it had reached its peak, it cranked up another notch and went again.
They say that live rock music comes in at 110 decibels and that a good old thunderclap is 120. The boffins reckon that a military aircraft take-off is 130 and a jet take-off is 150. It's hard to know how many boffins, if any, populate Celtic Park on Champions League nights, but it would be good to hear from them and get their numbers.
Because it was loud in the east end of Glasgow. AC/DC loud. AC/DC on a thundery night with 747s taking off all over the place. Only 20 minutes had passed when you started thinking that 60,000 tanks of oxygen wouldn't go amiss, one for everyone in the stand as they took in the breathless nature of what was happening down on the pitch.
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This was not what we'd expected. Maybe some did, but not many. Manchester City, with their £400m squad and their storied manager, hadn't conceded two goals in any of their 10 games so far this season and yet here they were, 2-1 down to Brendan Rodgers' marauders.
One-down in three minutes. The first time Pep Guardiola has known the sensation of trailing in a game as City manager. A training ground move that dynamited the visitors.
Look at it again and what you see is interesting. Slow it down and pause it. The ball is in the air from Scott Sinclair's free-kick on the left and already the Celtic cavalry are streaming in, leaving their opposite numbers behind them. There are four Celtic men in the box to City's one.
This is all pre-planned but what is planning without desire and execution? Sinclair did his job, James Forrest did his. Erik Sviatchenko didn't mean to nut his diving header on to Moussa Dembele's chest, but galloping away and screaming at the gods, he didn't look like a man who was overly disappointed with the outcome.
City given a fright
This was the howitzer that the game needed but which few expected. In those early minutes, City looked like a team in mild shock, as if the realisation was dawning on them that this was going to be a battle and not an exhibition.
Even when they equalised, they couldn't get to grips with the occasion. They hit Celtic and maybe they expected them to go down. They didn't. Celtic just hit back and made it 2-1.
It wasn't just the goal that might have stunned City, it was the quality of it. Nir Bitton's piece of impudence in the beginning, then Tom Rogic's run and weighted pass to Kieran Tierney who found the net via Raheem Sterling's boot.
We've seen Celtic do that to teams this season - to Kilmarnock and Motherwell and Rangers, easy prey on the domestic front. They've been hugely impressive in league action, but you wondered if these goal-fests were just examples of flat-track bullying or was there something else going on.
Goals at both ends
On Wednesday, we found an answer. Putting four on Aberdeen, five on Motherwell and Rangers and six on Killie was impressive, but what happened on Wednesday was on a different level. In 90 minutes, they put three on City, a team that had conceded just six times in the 900 minutes they'd played before coming to Glasgow.
In that one move they found a level of accuracy that eluded them for the entire game in Barcelona. After the drubbing at the Nou Camp, Rodgers was asked whether it was embarrassing or not. He said it wasn't but later recanted. It was an illustration of what can happen when you're passive in the face of brilliance. Rodgers said that the lesson had been heeded. He was right. That goal was further proof of it.
A good game quickly entered the realms of a great one. Celtic's attack is improving rapidly but its defence remains vulnerable. Before Wednesday, they'd conceded 22 goals in 15 games and those kind of numbers were surely ones that had the Silvas and the Sterlings and the Agueros licking their lips.
It was Silva's gorgeous pass and Sterling's beautiful finish that made it 2-2. Once more, you waited for City to drive on and disappear over the horizon, but it was Celtic who came again.
French striker Dembele? Formidable!
Tierney crossed and, in the absence of even vaguely competent defending, Dembele hooked Celtic back into the lead. Tierney turned 19 in June. Dembele hit 20 in July. These two have it in their gift to become Celtic legends if they stick around long enough. They'll have suitors, the pair of them. They announced themselves on the European stage in the rain of Wednesday night.
It's funny the things you remember on evenings like this. The goals, of course. The atmosphere, naturally. City pouring on the pressure in the closing minutes, after Nolito made it 3-3, and Celtic's unyielding response to that pressure.
There was a little moment eight minutes from the end that made you smile. Dembele, like some of his team-mates, was weary by then. If he was a car, the petrol light would have been on long since. City were threatening. The ball was with Pablo Zabaleta on the right-hand side of the pitch. Zabaleta was looking to make something happen. A run, a cross, a killer pass. As they say in the trade - he's capable.
Dembele stirred himself from 20 yards away, found the gas to come blasting in and ransacked the Argentine of possession. Having done the job, he took the roars of approval from his fans.
You looked at Dembele, thought of his two goals on the night, his five for the week and his 12 overall and you tried to place that one tackle, when jaded, among the good things he has done since becoming a Celtic player.
It wasn't a goal or an assist, but it spoke of hunger and honesty and, in its own way, it was outstanding. Just like the occasion. Much more of this and Celtic are going to have to put oxygen masks under the seats.