It was harder to tell who would be more relieved when Tom Rogic drew Celtic level for the second time, referee Craig Thomson or their manager Ronny Deila. The official made a critical error when he overruled assistant referee Alan Mulvanny’s decision to award a throw-in to Celtic down by the main stand when the ball had clearly come off James Tavernier's knee last. It may have seemed inconsequential at the time given the area of the pitch it was awarded in, but with one swing of Barrie McKay’s boot the ball nestled in the top corner, bringing the magnitude of Thomson’s error to bear. It was a clear and obvious mistake, and while credit for the goal should remain with McKay for his exquisite finish, there is no doubt that Thomson’s intervention was critical.

For the opening half an hour it looked as though Dundee United chairman Stephen Thompson would have more chance of receiving a Christmas card from Walter Smith than a player had of receiving a yellow card from the whistler.

He could and probably should have booked Gary McKay-Steven in the opening seconds for a wild lunge on Jason Holt in midfield, but chose to keep his cards in his pocket when the foul would surely have drawn a caution had it been committed at any other point in the game.

Andy Halliday then threw himself down looking for a penalty, but this time Thomson called it correctly as he waved away the weak appeal.

The referee seemed determined to keep his powder dry early on at all costs, as he again declined to card Dedryck Boyata for hauling down Kenny Miller after being caught in possession.

Quite how he didn’t book the big defender shortly afterwards for a blatant body-check on McKay is anyone’s guess, and coming after he had missed a clear corner for Celtic moments earlier, the errors were mounting up.

He could also easily have carded Dean Shiels for flattening Kieran Tierney late after the young defender completed a clearance, but with the precedent set, a warning was deemed sufficient.

Again the policy was maintained as a wild lunge by Scott Brown was punished only with a free-kick.

After half an hour though, lo and behold, eventually the yellow card was shown as substitute Erik Sviatchenko dived in on Shiels. Ironically, it looked as though there had been little contact on this occasion, but the caution calmed things down until the break.

The next booking didn’t arrive until the hour mark, but it was an easy one for Thomson as Dominic Ball hauled back Leigh Griffiths after gifting him possession.

Thomson was back in lenient mood though when he let Halliday away with a sliding lunge on Patrick Roberts, but he had no choice other than to card Stefan Johansen when the Norwegian chopped down Barrie McKay with quarter of an hour remaining.

Thomson then correctly waved away a soft-looking penalty claim for the second time in the match when Celtic substitute Callum McGregor went down far too easily under pressure from Lee Wallace.

The Rangers left-back then ran into Nir Bitton and went down holding his face, but again it looked as though Thomson called it correctly by ushering the Rangers man back to his feet.

A booking was shown to James Tavernier in the closing minutes as he tripped Patrick Roberts, and while that particular caution highlighted inconsistencies in the referee’s decision-making, all-in-all it had been a relatively quiet 90 minutes for Thomson.

But then, he decided to intervene in what looked like a straight-forward decision from his assistant, and ensured that he would be more than a mere footnote in the story of the game.