Amazingly, referee Stevie McLean and his back-up squad failed to spot the offence and the sense of injustice for Deila was fuelled in the second period when his team had Craig Gordon red-carded and folded to a 3-2 loss.
Deila said: “That Inverness semi-final game is still something I think about.
“The fact we did not get that treble in my first season is killing me, still.
“That referee’s decision in the semi-final, when the ball is punched off the line and then we get a red card and lose, it still hurts me now.
“That’s my only real regret. Would I still be there if we’d won that treble? Yes, I think so.
“That irritates me the most, losing that treble.
“We were very close, but I suppose that’s football. It was not our day.”
A year later, Leigh Griffiths hit the inside of the post and the underside of the bar and Patrick Roberts missed an open goal as the Hoops toiled to a 2-2 draw against Mark Warburton’s side after extra-time.
“I don’t mean I didn’t mind losing to them. I know it hurt everyone at the club and it hurt me, too.
“What I mean is we played so badly we didn’t deserve to win it.
“I didn’t recognise the team as being my team that day. There was no speed, no energy.
“That responsibility was mine. Right there at that point I realised my team was out there, but they were not having fun any more.
“I understood the pressure was too big to carry the team on.
“To me, being respected as a man is more important than anything, more important than being respected as a coach or a manager.
“Football should be fun and if I’m not having fun I’ll do something else.
“In the end, it stopped being fun because I didn’t feel I was having enough of an impact on the team. That Rangers (sic) semi-final confirmed it.”