Ten months and 53 games later, it ended on their own lush-green swathe in the east end of Glasgow with a 3-1 win over Dundee United.
In between, the roller-coaster season had many more ups than downs.
And, when the ride finally came to an end, Neil Lennon and his players had the league championship safely back in their possession for a third year, and the golden ticket to the Champions League qualifiers that comes with it.
They will start it all over again in mid-July, with the preparations kicking off when they report back for training on June 24.
Quite who will walk back in the door at Lennoxtown that day, only time will tell.
Georgios Samaras - who came off the bench to mark his final appearance after six years at the club by winning a penalty and converting it himself - was in tears as he took the applause of a support which has not always been so appreciative of the Greek enigma.
He then went on to confirm it was his way of saying goodbye.
Johan Mjallby, the assistant manager, has also left the stage, and his presence and influence will be sadly missed, most of all by Lennon.
But will the manager also be looking for replacements for Virgil van Dijk, Fraser Forster and a few other key cogs in the Green Machine?
Indeed, will Lennon himself be here for a fifth season?
If he decides to seek a fresh challenge, or is made an offer which affords him the opportunity he wants to test himself in England, the torch - or chalice - will be passed onto someone else.
What a challenge that promises to be, with the six games between now and the group stage of the Champions League a baptism of fire, given how they define the entire season for the Parkhead club.
If it is still Lennon who leads them into this early-season minefield, how well equipped will he be to safely negotiate it?
He has sought assurances from the board and major shareholder Dermot Desmond that his ambitions, not just to be involved in Europe, but also competitive, will be matched with investment.
He will meet with chief executive Peter Lawwell and other senior figures this week before heading off on holiday to set wheels in motion.
But how big will those wheels be, and will they take him where he wants to go?
"These talks will be to get things up and running," said Lennon.
Even before they sit down, Lenny knows that, as ever, the policy will be to caw canny with outlays until the club know if the big cheque from group stage qualification is once again on its way to their account.
He understands this prudence, thought that is not the same as embracing it.
The club punched above their weight when making it to the last 16 last season.
But, if they continue to hold back on spending, they will remain susceptible to a sucker punch in the qualifiers, with the damage this would bring leaving them reeling for more than a count of 10.
That's a number on the mind of the supporters, who reckon Lenny's side are now on course for 10-in-a-row, even if Rangers do make it back to the top division the season after next.
But Celtic are no longer measured by domestic success. It is on the European stage they are judged, and last summer's exits - though they brought in over £20milliion - left them vulnerable, as Shakhter Karagandy exposed.
Should they fail to make the group stage, would the fans who yesterday turned out in numbers not always seen this season and stayed to join in the celebrations accept as mitigation the handicaps the manager must operate under?
That's doubtful. What is not up for debate is that, without Champions League football, it would be a long and trying season, reflected in the numbers who turn up on a regular basis.
That, in turn, would undoubtedly impact on the performance of the players, and the calibre of signing the club could attract.
Lennon admitted he felt drained by it all and said: "What I want now is a break because I am tired.
"It has been a really long season, a marathon season, really.
"It will be nice to reflect on things and take stock on things and get ready again for when we come back in June."
He can take satisfaction from the fact he worked a miracle to keep everyone fully focused throughout this campaign, the European light having gone out long before those of the Christmas variety sparkled into life.
They lost only once in a 38-game league season, and finished on 99 points - 29 clear of second-placed Motherwell.
They cracked in 102 goals --the final three scored against Dundee United by Anthony Stokes, Samaras and, of course, Kris Commons.
They conceded only 25, Fraser Forster denied a final clean sheet when Filip Twardzik deflected a Gary Mackay-Steven cross past him in the closing minutes.
Overall, they won title No.45 in the style of real champions, and are already installed as favourites to enjoy a successful defence of the crown next season.
For all the feel-good factor which pervaded trophy- presentation day, the humanity which makes the club so special was not lost.
The Celtic fans, at Paradise for a party, found time to pay tribute to little Oscar Knox, the five-year-old supporter who last week lost his battle against cancer.
The Hoops and United players wore black armbands in their own tribute to the brave lost soul, and five minutes into the match, a poignant rendition of You'll Never Walk Alone was cued.
With old Bhoys John Hartson and Stiliyan Petrov - no strangers themselves to this horrible disease - in attendance to help with the title trophy presentation, it was a cold reminder of why every day should be celebrated, whether there is a tangible reason or not.