This video can not be played Police create cordon on pitch to separate Old Firm fans As if the ugliness of the 120 minutes wasn't enough - the grisly battle, the hair-on-fire panic, the abysmal lack of anything resembling coherence or even competence - there was the disgrace of the post-match.

Celtic had made it through to the Scottish Cup semi-finals after one shot on goal and no shot on target. They had survived their way through the day despite their own awful shortcomings, winning on penalties because Rangers were an abomination in reply. On a day of blocks, misplaced passes, crosses flying out of play, free-kicks wasted, aerial duels, hoofball, head tennis, punts downfield, unending fouls and a chronic lack of accuracy, the last act was Tomas Cvancara beating Jack Butland. Or, at least, we hoped it was the last act.

It wasn't, of course. The finale to the day involved a pitch invasion from many, many Celtic supporters at the Broomloan Road end. There were 7,500 of them at Ibrox. A return to the way things were pre-2018. Mistake. Big, big mistake. Initially, the Rangers fans in the Copland Stand reacted, a tiny number threatening to pile on to the pitch and head into the fray. They were shoved back in quick order. More Celtic people streamed on, dancing and waving and cajoling. Red rags to Rangers' bulls. Celtic staff beseeched them to clear off but their pleas were ignored.

Ugly scenes after Celtic beat Rangers on penalties to reach Scottish Cup semis Police separate Celtic and Rangers fans after Ibrox pitch invasion The Rangers dam burst. On they came from the Copland Road stand in big numbers. A menacing posse - many wearing masks - made a beeline for Celtic staff and players. One of the visiting backroom team was confronted - we can't say yet how violent that was - but the fan was jumped on by stewards and police led away. Martin O'Neill said later that the staff member was trying to prevent an incident happening - "it's why the person on the field was wrestled to the ground," said the Celtic manager. It was troubling, to put it mildly.

Next, another Rangers fan - or fans - squared up to Julian Araujo, the Celtic full-back. What was the extent of the contact? We'll have to revert to any footage that emerges, but it was shocking. O'Neill led Araujo away, a look of deep concern on his face. For a second, the threat of Rangers fans meeting Celtic fans was a real possibility. Mercifully, it was averted. Missiles flew, though. Certainly, there was a flare thrown from Rangers to Celtic. That was the first one. Other objects came back the other way. Watching the chaos you had to wonder about the logic of extending the numbers of away supporters, the obvious dangers, the unwise faith being placed in sections of these fans behaving themselves. Back to the drawing board on that one, you suspect.

The Scottish FA is investigating, as it needs to. Neither club said anything officially in the immediate aftermath. When they're of a mind to talk, they might want to address rumours of a bust-up between players in the tunnel. Cvancara had blood on his jersey. It would be helpful to know how it got there.

This video can not be played Watch Celtic beat Rangers on penalties in Scottish Cup So, not so much an Old Firm derby, more a demolition derby, a fittingly gruesome end to a lousy cup tie, a game that made the eyes bleed. Both of these clubs are pretty angry right now. They are playing catch-up with Hearts, a scenario they never envisaged in a hundred years. They're waiting and waiting for the Premiership leaders to implode but there's little sign of it. The league is far from done - there will be many more twists and turns - but the reality for Rangers and Celtic is that the Scottish Cup might be their best shot at silverware. The 1954-55 season was the last time both failed to win a trophy.

For Rangers, that chance has gone. They blew it, pure and simple. They had so much ball but so little invention and penetration. They could have been out there for two hours more and you wouldn't have backed them to score. The same for Celtic. They have an excuse for the hopelessness of their performance in attack (defensively they were really good). If they want to use it, that is. They were without Callum McGregor, their captain, their talisman, their consistent source of influence and class. No McGregor meant trouble for Celtic. On top of that they were missing Kieran Tierney, Kelechi Iheanacho and the long-term wounded - Cameron Carter-Vickers, Alistair Johnston, Arne Engels and Jota. That's five, maybe six, starters - all not there.

This video can not be played Martin O'Neill on post-match scenes at Ibrox Rangers had a relative clean bill of health by comparison. Plus home advantage. Plus a battalion of new signings who were supposed to bring energy and momentum to the second half of the season. They have spent big under Andrew Cavenagh's ownership. Knocking on for £40m - maybe more - has been splurged on transfer and loan fees. You wouldn't know it. Andreas Skov Olsen, 40 caps for Denmark, was their marquee loan recruit in January. He has been anonymous in his games so far and, if this was his big moment to announce himself, he flunked the test. His corner, in the 52nd minute, was a microcosm of the day. Right-hand side, packed penalty area, Celtic on the ropes, Rangers finding impetus if not accuracy. The corner was akin to a backpass, hit along the ground to the near post, where it was promptly hoofed away. The only thing that was holding up out there was Celtic's defence; firm and committed.

They headed and blocked and cleared. They scrambled when they had to. Rangers had so much possession but were lamentably dull in their use of it. Even still, you felt that at some point they'd make a breakthrough, at some point they'd find a chink and somebody would do something that resembled a clinical piece of play. Nobody ever did. Emmanuel Fernandez pretended he did when scoring 11 minutes into extra time. He wheeled away after the ball hit the back of the Celtic net, saluting the fans, applauding their support as he drank in the acclaim. It was all a con. Fernandez scored all right, but it came off his left hand. Claiming it as legitimate was a desperate act of a desperate man in a desperate team.

Ugly end to engrossing Old Firm quarter-final Scottish Football Podcast Meanwhile, more than 100 minutes in and Celtic had still not had a shot on target. Pitiful. Some might call the stalemate and the passion and the thud and blunder compelling, but you have low expectations if that's the case. Even allowing for their missing players, Celtic, from midfield to front, were a dismal shadow of what they want to be. Up front, they have little to no threat. They have recruited strikers and none of them, seemingly, have much ability to strike. Last weekend, in the Premiership, this pair served up a fine game with some excellent football and memorable goals. This was a grunt-fest. Great, if that's your kind of thing.

To penalties and, for Rangers, the writing was on the wall when James Tavernier began by hitting the crossbar. Djeidi Gassama's effort at 3-2 to Celtic - ballooned over Viljami Sinisalo's goal - set the stage for Cvancara to end the contest and spark the invasion. An hour after the trouble ended and after everybody had left Ibrox, the sound of sirens could be heard regularly. Out there in the real world there was a fear that the toxic atmosphere would continue.

So much to ponder, then. Not the football - please, no - but the scenes in the aftermath, the footage that might reveal the precise nature of some of the most unsettling stuff went on, and a wait for what the authorities have to say about it.