The only thing is it was supposed to be Juventus who confirmed to Neil Lennon how far his team has come and what work is still required.
Today, the Hoops boss is coming to terms with the fact it was St Mirren who got there first.
And, as one Lennon mulls over what went wrong and, more importantly, what he can do to put it right, his namesake, Danny, is contemplating how he can build on Saints' 3-2 win in the Scottish Communties League Cup semi-final.
Make no mistake, they deserve their chance to take on Hearts on March 17. They outfought, outran, outjumped and outscored a group of individuals who Neil Lennon described as an imitation of the SPL-topping side with a treble in their sights.
The only treble which was delivered was of the Hampden horror variety.
This defeat makes it an unwanted 10 months for Celtic, having previously lost to Hearts in the William Hill Scottish Cup semi-final in April and to Kilmarnock in last season's League Cup final.
At least in the final back in March, Lennon could console himself that his team played reasonably well but, on the day, had come up against a keeper in inspired form.
Yesterday, Craig Samson had no need to emulate the heroics of Cammy Bell – because Celtic rarely got a shot on target.
As much as St Mirren played as a unit, with their outstanding performers Steven Thompson, young John McGinn – ironically the grandson of former Parkhead chairman, Jack McGinn – and defender Jim Goodwin, a man told he was not good enough for a career at Parkhead, Celtic were the architects of their own downfall.
And what a fall from grace it was.
Lennon insisted this was as poor as his team had performed for him domestically, and no one could argue with that blunt assessment, which he delivered shortly after giving his players chapter and verse in the dressing room of despondency.
It was the fifth time in nine visits to Hampden as Celtic manager that the Northern Irishman has left bitterly disappointed.
Against that, Lennon has masterminded four wins at the National Stadium. But placed against his overall record as a manager, both domestically and in Europe, it is a poor strike rate, and one which he makes no attempt to dismiss as irrelevant.
He is, however, largely powerless to influence matters once his players cross that white line, and they are the ones who must look in the mirror today and ask themselves if they could have done more.
It's not as though they turned up at Hampden unprepared, or out of form. The two games since the mid-season break brought a 4-0 win over Dundee United and a 4-1 win over Hearts.
Why travelling the short distance to Hampden should create such a dilution of this level of performance is the real mystery.
If it is complacency, then surely the results on their previous visits would act as an antidote.
If it is a lack of understanding that, every time they take the field wearing Celtic colours they must give 100%, no matter the competition, Lennon is the man to show them the error of their ways.
How can a player like Victor Wanyama, coveted by top clubs and adorned with a valuation which could sustain a small community for a year, look so ordinary?
How can Goergios Samaras, such a hero in the Champions League run which has carried them to the last 16 encounter with Juventus, struggle to make the simplest of passes?
How can Charlie Mulgrew, one of the very best exponents in the country of set-pieces, perform quite so unconvincingly from the spot when presented with the chance to put Celtic ahead just after half-time?
To be fair to the three aforementioned players, they were joined by the vast majority of their team-mates, Lennon exonerating only Gary Hooper, who got them off the mark with an equaliser on the stroke of half-time.
By then they had trailed for most of the half to a goal from new Buddies' signing Esmael Goncalves, who could not have dreamed of such a start to his career in Scotland.
The welcome afforded to him by the Celtic defence was more than generous, standing aside as he latched on to a Conor Newton lob into the box.
That was the first goal scored by Saints against Celtic since Danny Lennon took over as manager eight games ago.
By the end of play, they had trebled that strike rate, with Paul McGowan showing Mulgrew how to convert a penalty after the Celtic defender had handled a Gary Teale cross, then Thompson showing tremendous agility to swivel and hook a Marc McAusland cross beyond the reach of Lukasz Zaluska to put Saints 3-1 ahead with 22 minutes still to go.
The expected response from Celtic was as disappointing as it was futile, Mulgrew finally finding his range with the final kick of the game deep into injury time.
Too little, too late. Celtic had blown another opportunity to home in on a treble, and it is St Mirren who have the chance to pick up the first piece of silverware of the season.
Celtic? They are left to pick up their chins, and re-establish the faith their manager placed in them before this latest bitter disappointment.
He had warned semi-finals are always on a knife-edge. Yet again, this one has delivered a dagger to Lennon's heart.