Having fought through two qualifiers and a play-off just to get there, Celtic were entitled to behave like they were in the San Siro for the party. Today's hangover, though, will be a painful one.
And Fraser Forster's more than anyone's. The giant shot-stopper struggled through the latter months of last season and the early weeks of this one without ever capturing the form he showed in the compelling environment of the Champions League last time round.
Yet for large chunks of last night's display he was not the only one for whom the famous tournament theme tune seemed to stir memories; both Gary Hooper and Victor Wanyama took to Twitter to send wistful best wishes to their former colleagues.
Even the bright lights of the Barclays Premier League pale in the glare of Europe's elite competition.
It was a competition last term where Hooper, Wanyama and Forster formed the spine of a Celtic side who raised more than a few eyebrows in the Champions League.
All three cemented growing reputations and firmly made their mark in the competition with impressive performances in the most demanding arena of all.
Last night, Neil Lennon's side found that they still have a bit of backbone when it comes to holding their own among celebrated company.
Forster, like Kelvin Wilson, Wanyama and Hooper, could well have been off this summer too, a loss that the Parkhead side cold ill afford.
Celtic were forced to write a letter to Benfica warning the Portuguese side against tapping up the English keeper, whose body language in recent weeks has appeared to betray his real thoughts on remaining in Glasgow for at least the next few months.
However, if anything can revitalise the keeper and re-ignite the form that saw him repel the likes of Barcelona last season, it is the glamour and unique pressure of the Champions League.
Last night may have served a painful reminder of how cruel the game can be at this level - and Celtic have known a few cruel nights in this competition on the road in the last decade - but there were just as many positives for Forster and for Celtic to take out of their encounter.
With his country off to the World Cup in Brazil this summer and Forster on the periphery of Roy Hodgson's England squad - coupled with Joe Hart's form has been less than convincing - the keeper will do his chances of inclusion no harm at all if he can hold his own in the Champions League.
For large chunks of last night's game against AC Milan, it looked as though he had found the energy to aim for last season's heights.
Ultimately, even as the home side drove home their second goal of the night, he was still able to get an impressive hand to Mario Balotelli's free-kick before Sulley Muntari bundled in the rebound.
Beaten just minutes before by Emilio Izaguirre's deflection, Forster could perhaps seek to vent his frustration by suggesting that if forwards don't take chances then keepers and backlines are always left vulnerable.
Blameless on a night in which they lost two goals in the late stages of the game, he can once again reflect on the fact he is a goalkeeper who can perform at the top level.
There were four minutes on the clock when he had to batter away a fierce Balotelli drive, an early opportunity that briefly looked as though it may open the floodgates for a sustained period of Milan pressure.
After Balotelli came Cristian Zaccardo with an attempt that Forster had to stifle before he was called into a block from Valter Birsa.
Yet, once those frantic opening minutes had faded he suddenly found himself with time to take stock as Celtic slowly impressed themselves with a quiet composure on their Italian opponents.
Still, Forster had to look sharp again when he got one hand to an Alessandro Matri header while as the opening half drew to a close, a deflection from Efe Ambrose meant he had to get down swiftly to turn the ball around his post.
Muntari really should have got one past Forster in the second period when he somehow contrived to head wide with the goal gaping.
When they came, the goals winded a Celtic side who gave so much and took nothing.
Forster lay slumped on the turf, dejected and studs tangled in his own net as Milan betrayed their relief with some frantic celebrations.
Once he has picks himself up, he'll appreciate there is time yet for heights to be scaled in this, the most challenging of environments.