The unforgiving nature of the Champions League was impressed upon Celtic in cruel fashion at the San Siro when a fighting performance that saw Anthony Stokes strike the crossbar was upended by two late goals.
The first came from Cristian Zapata which clipped Emilio Izaguirre and left Fraser Forster wrong-footed, and the second a free-kick from Mario Balotelli, blocked by the goalkeeper, which fell for Sulley Muntari to turn across the unguarded line.
Now Neil Lennon and his players face the fearsome task of having to take something from their next fixture, the visit of a Barcelona side who mercilessly dealt Ajax a 4-0 hammering in the Nou Camp, with a hat-trick from Lionel Messi to boot.
The question answered by the first glance at the team sheet was how Lennon would deal with what had been anticipated widely as a choice between Georgios Samaras and Stokes. In the event, he found accommodation for both, with Stokes allocated the spearhead role while his Greek colleague was posted in left midfield.
Joe Ledley failed to make it off the casualty list and was replaced by Charlie Mulgrew, meaning that – along with a start for Samaras – Celtic showed two changes from the side who beat Hearts 3-1 last Saturday. Milan were forced to alter their disposition from the 3-4-3 they played against Torino later the same day.
Kaka, lately restored to San Siro for a second spell with the Rossoneri, was ruled out through injury, along with captain Riccardo Montolivo, defenders Ignazio Abate, Mattia De Sciglio and striker Stephan El Shaarawy. Still, there was menace enough in the forward pairing of Balotelli and Alessandro Matri.
Balotelli duly bookended the first half with shots which forced Forster into big saves although it is doubtful that the goalkeeper knew much about the former Manchester City man's first attempt, a venomous volley from the edge of the box.
Forster parried it with both hands but he would have been in real trouble had the effort not been directed straight at him.
Luck, though, seemed about to favour Balotelli in injury-time, when he tried a speculative low drive which lacked either the power of direction to confound Forster until it took a menacing deflection off Efe Ambrose and was heading inside the far post until the 'keeper hurled himself full length to divert it just wide for a corner-kick. The menace had not spent itself, however, as Celtic's attempt to clear fell to Muntari, but although the midfielder fuelled his drive with power, it whipped narrowly over the top.
The conclusion to the first half confirmed to Celtic that their concentration would have to be unflagging throughout, but they also had substantial ground for satisfaction as they made their way to the dressing-room. For a start, they had edged the greater share of possession and they had forced twice as many corners as their esteemed opponents – four to Milan's two. That said, the ratio of shots on and off target significantly favoured Milan.
Within seconds of the restart, Kris Commons doubled Celtic's tally in that department when he broke free into the box but slashed his left-foot drive wildly askew.
Samaras had a similar sight of the target when he burst through the centre and he responded with a fiery drive which curled in flight just enough to carry it wide of the mark.
Milan could not be expected to allow Celtic to increase their ambition without some attempt at a condign response and they were aided by the game's stretch as play rebounded from box to box, with Balotelli prominent.
The increasingly open nature of the contest, though, also allowed greater space to Celtic, whose movement and use of width was impressive and fluent and was exploited on one occasion by Scott Brown, who penetrated the Milan box only to have the ball nicked off the toe of his boot as he was poised to take his chance.
Milan's response was a dangerous deep cross from Kevin Constant which hung beyond the back post to be met by Muntari, but the midfielder pushed his header over.
The denouement unfolded with mesmerising speed, beginning with a Stokes free-kick which cleared the wall and beat Christian Abbiati but cannoned off the crossbar and out.
Within three minutes Milan were in the lead and three minutes later saw Muntari stow the points safely away as Celtic crumpled in despair. (© Daily Telegraph, London)