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.