Only three minutes were left when Anthony Stokes, the creator of James Forrest's Champions League injury-time clincher against Shakhter Karagandy in midweek, twisted away from two men on the edge of the box and tumbled over Stuart Armstrong's outstretched leg.
In front of the watching Teemu Pukki, the club's £2.4m signing from Schalke 04 - and quite possibly the man earmarked to take Stokes's place - the Irishman curled in a sweet free-kick which struck the inside of Radoslaw Cierzniak's right post, and traversed the line before hitting the opposite sidenetting. It wasn't the worst way to bring up your half century of goals for the club.
Whatever other strikers and left-backs were arriving at the club prior to last night's closure of the transfer window, manager Neil Lennon restated that getting the Irishman's signature on a new contract beyond this summer was a priority, and said Emilio Izaguirre - who threw his shirt into the crowd at the end - was going nowhere. "I don't think the kid [Stokes] can do much more than what he is doing at the minute," said Lennon. "I am hoping to get that tied up. He is very important for us just now."
"Competition is good for everybody, it keeps everyone on their toes," said Stokes. "But obviously I want to keep myself in the team."
Not everyone was quite so content, however. United boss Jackie McNamara last night railed against referee Crawford Allan for failing to notice that Stokes had shuffled the ball back a foot or so after the award of the decisive free-kick, to allow him room to get the ball over the wall then down again. There was also a heated exchange between the two managers - old pals of course from their playing days - about the referee stopping each half before corners could be taken, for Celtic in the first period and United in the second. They also disagreed about whether a Gavin Gunning challenge on Mikael Lustig, which led to the Swede being stretchered off with an ankle problem, was "reckless".
"We had a free-kick on the edge of their box and we didn't feel the wall was far enough back," said McNamara. "Then Celtic got a free kick - whether it was a free-kick or not, I'll need to have a look at it - and Stokes has moved the ball back a few yards to gain an advantage and the referee hasn't spotted it. Those two or three yards are the difference to it going over our wall. I would say a reckless challenge would be Scott Brown's on Stuart Armstrong."
The Parkhead side made three changes from the side which won in midweek, with Georgios Samaras, James Forrest and Charlie Mulgrew excused after their week's exertions in favour of Virgil van Dijk, Derk Boerrigter and Izaguirre. All three had a point to prove - not least the giant Dutch centre-half, after a couple of early mis-steps in his Celtic career - but a couple of forays from the former Groningen player showed precisely what he had to offer going up the field. The first saw him run umolested fully 70 yards to fire over the bar, while a second effort whistled narrowly wide. It was all part of a lively start from the visitors in which a Stokes volley narrowly miss Radoslaw Cierzniak's bottom corner.
Lennon said Van Dijk had set a standard with this performance but both he and central defensive partner Efe Ambrose were posted missing when Stuart Armstrong's floated cross picked out David Goodwillie in the box after 24 minutes. The on-loan Blackburn man's header was too close to Fraser Forster, however, and the Englishman re-inforced his importance to Celtic ahead of the closure of the English transfer window tomorrow with a fine parry from Nadir Ciftci's free-kick.
Amido Balde entered the fray for the stricken Lustig, a signal that Celtic would go long to circumvent the dry, slow pitch but at the other end, young Andrew Robertson, not content with keeping Boerrigter quiet, was able to send in a wicked cross which was missed by everyone.
Boerrigter lasted until the 83rd minute before he left the proceedings with an injury, a time when Celtic were mounting a late charge. Balde headed wastefully wide from a corner, a couple of penalty claims came and went then Commons fired inches past after more good work from Stokes. But Celtic kept at it and eventually got their reward. Right on deadline, you might say.