Five years ago they were about to become the most unlikely of the History Boys.
On Saturday Brendan Rodgers led his side to 63 matches unbeaten but a signature or keynote victory has so far proved elusive in Europe.
Points have been taken from Manchester City and Bayern Munich frightened but wins over Barcelona don’t come along often enough.
Even after giving Barca a scare in the Nou Camp a couple of weeks earlier the hoops shouldn’t have stood a chance against Lionel Messi and his mates who were playing a brand of football that no one in Europe could live with.
When Neil Lennon got round to picking his side there were some notable names missing such as Scott Brown, Gary Hooper, Anthony Stokes and Emilio Izaguirre. Those four players are heavily associated with the successes of that period but were all unavailable for the big match which fell a day after Celtic celebrated their 125th anniversary.
Most fans asked to name the starting XI can tell you straight away that Miku started- just another twist in an incredible story.
Celtic have only won twice at home in the Champions League since that win over Barcelona, hopefully eleven more heroes will emerge next month when Anderlecht are put to the sword.
FRASER FOSTER
The yellow wall had his career transformed by two matches against Barcelona.
The former Newcastle man was in great form in the Nou Camp and was kept just as busy in the home leg.
It took a late goal from Messi to beat the keeper but that was a minor detail with Foster even providing an assist for Tony Watt’s winner.
MIKAEL LUSTIG
The only survivor from that side still at the club, he’s been through a lot since and still loves winding up opposing players and fans.
There weren’t many attacking opportunities for the Swede but he stuck to his task, closed down space and did what was required before making way for Watt.
Five years on he’s eyeing up a double over Anderlecht and the prospect of a tasty run in the Europa League.
KELVIN WILSON
A strange signing and a strange Celtic career.
Wee Billy Davies put his foot down on a move in January 2011 but signed on a free during the summer transfer window.
Many of his best performances were in Europe but he returned to Forest 18 months later, at the age of 32 he hasn’t played a competitive game in the last year.
EFE AMBROSE
A highly unlikely defensive partnership with Kelvin Wilson provided the backbone to this victory.
Later in the competition it all went south against Juventus but at this stage Ambrose was regarded as a sound reliable defender.
He has now been reunited with Lennon at Hibs and seems to be going from strength to strength.
ADAM MATTHEWS
A classic example of where did it all go wrong?
At left-back on the night he barely put a foot wrong and really should have gone on to enjoy a fantastic career at Celtic or elsewhere.
A clash with Keith Lasley the following season triggered a run of injuries with a move to Sunderland proving disastrous.
KRIS COMMONS
Loved the European nights and always found something special to produce.
Like Kelvin Wilson he took the step up from Nottingham Forrest in the Championship to Celtic in the Champions League in his stride.
In the final group match he stepped up to take the penalty that took Celtic through above Spartak Moscow, there was still work to be done despite beating Barca.
CHARLIE MULGREW
Played the holding midfield role perfectly, very disciplined and barely wasted a pass.
At time he was an additional central defender but he never dropped too deep and kept close to his twinkle toed opponents.
He left the club in 2016 but now finds himself playing in the graveyard that is League One with Blackburn Rovers, the Barca season was his best at the club.
JOE LEDLEY
Another player who put the team first and turned in an exceptionally disciplined performance.
There was nothing fancy or showy about his performance but he stuck to his task and gave Barca’s celebrated midfield little space to work in.
In 2016 he helped Wales reach the semi-final of the European Championship and is now playing his club football with Derby County.
VICTOR WANYAMA
His performance, like that of Fraser Foster, opened the door to Southampton.
The African was a giant on the night with his power play noted by scouts across the world, highlighted by the opening goal of the game.
After Southampton he moved on to Spurs and doesn’t look out of place in one of the most exciting teams in the EPL.
GEORGIOS SAMARAS
Was in the middle of an incredible run of form and goals after being redeployed wide on the left with opponents unsure how to deal with the gangly Greek.
Neil Lennon’s faith was repaid during this campaign as he rose to the occasion with goals from the qualifiers all the way through.
This was as good as it was to get, after leaving Celtic in 2014 his career took in various outposts but the footballing highlights have been rare.
MIKU
He signed on loan at the end of the transfer window but never really settled with Celtic just another stop off in a wandering career.
Without Gary Hooper or Anthony Stokes he led the line with the benefit of previous La Liga experience against Barca.
Miku played the game with intelligence working off thin pickings on the night, this result was to be the highlight of his Celtic career.
SUBSTITUTES
Tony Watt replaced Mikael Lustig and the rest is history. Unfortunately for Watt he never got to start another Celtic match as a striker and is now playing for his third Belgian club at OH Leuven.
Beram Kayal took over from Georgios Samaras while Marcus Fraser, John Herron, Dylan McGeouch sat on the bench with Lucasz Zaluska.