This wasn’t simply a convincing Old Firm victory, it was one of the most comprehensive beatings this fixture has witnessed in a very long time.
In many respects, this was probably the biggest 90 minutes of his 19 years in management.
Had Derek McInnes suffered defeat on derby day at Ibrox yesterday, then the knives would have been out for the Rangers boss all over again.
Beating Celtic and eliminating them from the Premier Sports Cup at the quarter-final stage was perhaps an absolute necessity for McInnes and his relationship with the club’s supporters.
But overpowering them in such a devastating, relentless fashion? Well, not even a manager of McInnes’ extensive experience could possibly have anticipated that.
This wasn’t merely an impressive Old Firm triumph, secured by a three-goal margin.
It was one of the most one-sided hammerings this fixture has witnessed in years, and at no stage did it seem as though Celtic had even the slightest foothold in the game, never mind a spell of control or superiority.
Before it was finished and they were permitted to retreat inside to lick their wounds, some serious questions were already being raised about the resilience of the champions and their capacity to retain what belongs to them this season.
The League Cup was not included in the collection. That was permitted to disappear during the Wilfried Nancy fever dream.
But Martin O’Neill somehow managed to rescue a top-flight title and Scottish Cup Double from the Frenchman’s disaster and yesterday the Northern Irishman seemed completely bewildered by everything unfolding before him.
He had no solution to it and neither did the players he had chosen, with one or two appearing unnerved by the occasion.
And yet it is possible that, somewhere in the back of his mind, O’Neill may have sensed that something along these lines was coming.
O’Neill had appeared almost consumed by this approaching double-header during the weeks beforehand. His team may have been producing victory after victory at the summit of the table, but the experienced boss had been unusually irritable throughout.
It was almost as though he recognised that something extra would be needed if Celtic were to make it safely into and out of Ibrox on derby day.
Even so, there were still problems for the old fox to address.
He chose to start Sam Johnstone in goal ahead of Viljami Sinisalo and, perhaps more unexpectedly, retained Sebaastian Tounekti on the left wing.
Kasper Hogh also spearheaded O’Neill’s attack, resulting in Camilo Duran operating on the right side of Celtic’s front three. That left Haissem Hassan occupying a place on O’Neill’s bench. In truth, the whole arrangement appeared somewhat confused.
McInnes, by contrast, produced a tactical surprise by introducing James Penrice as an additional midfielder and setting Rangers up with a back three, using a man-for-man system to contain Celtic’s attacking threat.
Because of the alteration, it seemed as though Rangers had an additional player in almost every section of the pitch, with Ryan Naderi and Kevin Kelsy imposing themselves physically and creating major difficulties for Celtic’s defence.
Johnstone, strangely enough, was also adding to their problems with a shaky, uncertain, mistake-filled performance which could – and arguably should – have resulted in Rangers scoring twice before the interval.
His first error was a poor clearance directly into the path of Kelsy, who should have punished the goalkeeper but hurried his effort and pulled it wide of the Englishman’s post.
His next mistake was an awful attempt to punch away a hanging Penrice cross, and it required an excellent goal-line clearance from Liam Scales to stop Misun Kim from capitalising on the error with a low, powerful first-time strike.
Misun, for his part, was finding it difficult to match the intensity of this frantic derby, failing to clear the first man with a couple of corners and sending a free-kick delivery far too deep, much to the audible frustration of the supporters.
Still, it felt as though the opening goal was inevitably approaching.
When it came after 21 minutes, it almost lifted the roof from the old stadium.
First, Naderi used his strength to get into Cameron Cartner-Vickers as the American dealt far too casually with an isolated attacking move.
Naderi not only dispossessed the defender but showed excellent awareness to quickly feed the ball into Kelsy’s feet who, in turn, rolled it into Neil’s path.
The skipper lifted his head, selected his target and calmly placed a finish beyond Johnstone’s reach and inside the goalkeeper’s right-hand post.
From that point, or perhaps even before then, there was little genuine doubt about how this tie would finish.
O’Neill tried to spark his team into action at half-time by withdrawing the badly out-of-sorts Tounekti and bringing on Hassan. The Egyptian at least provided Rangers with something to consider on the right flank, but not enough to alter the overall shape of the contest or shift its momentum in any meaningful way.
If anything, Celtic looked increasingly anxious and fragmented as Rangers continued to attack them in relentless waves of blue.
Minsu almost gave the second half a spectacular beginning with a powerful effort which forced Johnstone into an impressive save, but it was one of very few positive moments for a goalkeeper now clearly struggling with his confidence. He was soon required to make a double save when Misun and then Djeidi Gassamma threatened his goal following more excellent midfield work from Neil.
As the hour approached, Rangers did eventually find their second when Kelsy hammered a shot into the net at the back post after Gassama and then Penrice had dismantled Celtic down the left.
Not long afterwards, £11m signing Hogh was withdrawn for Alex Oxlade-Chamberlain. It was almost the first occasion on which the Dane had made any real impact and that will provide O’Neill with further concerns as he prepares for another huge battle on Sunday at Celtic Park.
With 75 minutes played, this opening derby of the season became even more comfortable and enjoyable for the home supporters as Neil fired in a third goal from the edge of the penalty area.
It was far more than McInnes could have imagined, but a disastrous evening for O’Neill, who now faces some significant decisions ahead of Thursday night’s Europa League clash with Ferencvaros and Rangers’ return to the east end next weekend.