Crowd trouble marred Celtic's dramatic penalty shoot-out victory over Old Firm rivals Rangers which secured them a spot in the Scottish Cup semi-finals.
Fans of both clubs spilled on to the pitch at full-time and launched missiles at one another as the police were forced to break up the violence.
This was the first time travelling supporters had been allowed the traditional away allocation of 7,500 tickets in eight years.
Despite failing to register a shot on target in 120 minutes of goalless football, last year's beaten finalists Celtic found a way to win again. Rangers captain James Tavernier hit the bar with the first penalty before fellow substitute Djeidi Gassama blazed over, with Tomas Cvancara then sealing the victory as Celtic ran out 4-2 winners from the spot before dozens of their fans invaded the pitch.
That sparked an invasion from hundreds of Rangers supporters and missiles were thrown as police and stewards moved to form a barrier. Flares were thrown and some minor skirmishes appeared to take place before order was restored and the away fans were left to celebrate alone.
With league leaders Hearts, cup holders Aberdeen and fellow top-six sides Motherwell and Hibernian already out, Martin O'Neill's Celtic are now red-hot favourites to lift the trophy. They will play St Mirren, who beat Partick Thistle 2-1, in the last four, with Falkirk up against Dunfermline in the other semi-final.
Danny Röhl's Rangers are now out of both domestic cup competitions and Europe, meaning the league title is their only remaining hope of lifting silverware.
The crowd trouble started well before kick-off as ticketless Celtic supporters forced entry to the Broomloan Stand, causing Police Scotland to close the turnstiles for a short period of time.
On the pitch, the match started in similar to fashion to last week's league clash at Ibrox with the home side well on top.
Celtic were missing captain Callum McGregor and Kieran Tierney following injuries picked up in the midweek win at Aberdeen.
Luke McCowan came into central midfield, while Liam Scales moved to left-back as Auston Trusty returned amid a three-match league suspension. Daizen Maeda started through the middle.
There was also a notable omission in the Rangers team as John Souttar was dropped to the bench along with Tochi Chukwuani.
The hosts forced the early pressure and there was a flashpoint when Trusty blocked Youssef Chermiti's strike with an arm. But it was tucked into his body and video assistant Andrew Dallas did not summon referee Don Robertson to the monitor.
Rangers were well on top in the opening quarter but that was the only real scare Celtic had and the visitors grew into the game.
The away fans were celebrating 10 minutes from half-time when Maeda netted with a diving header but Scales was ultimately ruled offside by VAR after heading on McCowan's cross. It was one of the few times that Celtic threatened in the match.
Dujon Sterling and Chermiti looped efforts over before the break and Rangers spent most of the second period in the Celtic half.
Hoops goalkeeper Viljami Sinisalo stood up well to the aerial pressure and came off his line quickly to foil Chermiti following a mistake from Benjamin Arthur. The visitors needed some last-ditch blocks from Trusty and Sebastian Tounekti in particular to keep the scores blank.
Rangers' physical advantage was forcing Celtic back and there was little respite for the visitors, who ended the 90 minutes with an all-new front three of Joel Mvuka, Cvancara and James Forrest.
The pattern continued into extra-time. Substitute Dane Murray's block denied Chermiti and Rangers then had a goal disallowed by VAR after the ball went into the net off the hand of Emmanuel Fernandez following a corner.
Chermiti volleyed wide from a good chance and Sinisalo saved from Nedim Bajrami as the action continued to flow one way, with Rangers ending the 120 minutes with 24 shots to Celtic's one.
Rangers won the toss for the spot-kicks but could not take advantage in front of the Copland Road Stand.
Rangers captain Tavernier went up first, but his effort smacked the crossbar and flew over.
Goalkeeper Jack Butland, who had saved eight of his previous nine penalties couldn't get near any of Celtic's four expertly dispatched kicks.
Gassama also saw his effort go over the top as Cvancara kept his goal to win the shoot-out 4-2 and spark chaos inside Ibrox.
Celtic supporters came onto the pitch to celebrate the result before a counter charge came from the home support.
Police and security intervened as the players were escorted off the field of play while both sets of fans launched missiles and pyrotechnics at one another.
The ugly scenes have since been condemned by the Scottish FA, who have vowed to carry out an investigation in line with Judicial Panel Protocol.
Celtic boss Martin O'Neill speaking in his press conference on whether the pitch invasion overshadowed the win:
"That would be a worry for me. The fixture itself, although still a phenomenal fixture, had lost a bit of its lustre because the away fans or full complement of away fans were not allowed in.
"We have no idea what might happen. I think today, with the crowd and our crowd there, to me, it was a proper Old Firm game in that sense. We will see what develops.
"It's a big derby game and I think there was a lot of jubilation at us winning. The fans spilt over and I suppose it is very difficult to quell that, I don't know.
"As we were making our way back, there was some kind of fracas and someone had tried to get on the field. I don't know, all I saw was a bit of a scrum down at the bottom.
"As you say, maybe it does taint proceedings but I think there was an element of self-protection in that one. I am making judgements on things I only half saw. From my viewpoint, it was a great win for us. Rangers are very strong and had the full week to go at it."
Rangers boss Danny Röhl speaking in his press conference about the pitch invasion:
"I was not on the pitch in the moment, I did not see it until now.
"I think we all know the emotional situation after a game. Nobody likes to see this.
"It was a great atmosphere for 120 minutes and should be like this, the other things should not be in the stadium or in football."
