It was the result that could finally spell the end for Neil Lennon at Celtic as his Hoops side were schooled by Ross County on home turf.
It sent a four-year run of 35 unbeaten cup ties crashing to a brutal end.
And prominent former players in the media are confident that this could be the end of the road for Lennon's second term in Glasgow with a run of two wins in 10 matches.
A fairly disgusted Alan Stubbs began the post-mortem on Premier Sports at Celtic Park, as he predicted an "interesting few hours" following the final whistle.
He wasn't wrong as hundreds of fans took to the area surrounding the stadium with police called to quell the anger.
Here's how the pundits saw it.
"We’ve heard a lot of talk about what Celtic need to do, Neil’s had a really productive meeting with the power-brokers, the players have come out and said they’re right behind the manager.
"That performance, I’m afraid, there’s a difference of opinion.
"Because when you want the players to show and prove that they’re right behind the manager, they haven’t done it today. It’s as simple as that.
"You can dress it up as much as you want. They’ve not produced, and this is a damning result for Celtic.
"There were a lot of people during the week saying, ‘he’s got until the cup final’.
"It will be an interesting few hours after this game tonight what happens."
"Neil Lennon has been badly let down by his players but he can’t survive this. He’s been a great servant to the club.
"The people protesting outside Celtic Park can’t call themselves Celtic fans. True Celtic fans wouldn’t be singing despicable songs about a man who has given the club the service Neil Lennon has. They are a disgrace. Self entitled a**es."
" Celtic, I don’t expect anything else from the players and Neil Lennon in terms of what’s been said. Not just since the Sparta game, but in this recent run they’ve been on.
"But the only way they can alleviate those concerns that people have got is by getting results.
"Every time they come on the park and they don’t get a result, and they don’t get a performance, it just heaps more pressure. And the words become very hollow.
"It seems as if they don’t have the answers. That’s the first occasion I’ve felt watching Celtic as if they don’t actually have the players now. It’s a ridiculous thing because they have so many quality players but the balance is not in the team.
"When you watch this side, they’re looking for so much to come from those wide boys, Elhamed and Laxalt.
"There wasn’t enough intelligence in how they were trying to play and they are desperately missing the likes of James Forrest and Mikey Johnston."
"I couldn't see it coming to be honest with you.
"I thought Celtic would bounce back from the big disappointment of their midweek European result against a side that equally have been struggling a little bit.
"I couldn't see anything other than a Celtic victory here. That is a major, major shock.
"The first thing I have to say is that everybody knows what I am and where I come from but I have to give you an honest appraisal of what I think is happening and going to happen.
"It's going to be very difficult for Neil to keep his job now. And I take absolutely no pleasure in saying that at all.
"I have been in that position and it's a horrible position to be in when it starts affecting your home life and your family which is what will be happening to Neil right now.
"Getting back to the bigger picture I think it will be very difficult to keep his job.
"I know he got the vote of confidence after a phone call with Dermot and Peter.
"But if you're asking me if today's result has changed things I'd say it probably has.
"Only time will tell, of course."