However, while confirming his side were second best that September day, he has bullishly defended some of his tactics and believes Rangers are in a far better place as they prepare for Sunday’s Betfred Cup semi-final against their fiercest rivals.
Warburton, pictured below, feels four clean sheets in five matches are evidence that they have improved defensively and believes hard work on the training ground will manifest itself at Hampden.
He said: “It’s a huge game in terms of significance, it’s another Old Firm derby.
“Everyone is aware of the significance, and the fact there’s a cup final place at stake only adds to that.
“It raises the stakes for everyone and we’re looking forward to it. What we had to do after the last Old Firm game was go away and work harder.
“We had to improve the consistency of our performance and I think that’s what we’ve done. We know we are getting better and better.
“We’ve worked really hard because that’s the only answer in trying to win games of football.
“It was a very heated discussion when we went over the game as a squad because the local boys know what it takes.
“They understood it and it was important to relay that message to the new boys coming in. You lose an Old Firm game 5-1 you’d better recognise what we have to do now because you don’t want to feel that way again.
“That was an awful feeling. That would fire up any player. If you have a poor performance with the ramifications to that level you remember it for a long, long time. I don’t want that feeling again.
“I didn’t go out at all after the game – not even to Waitrose, which is 100 yards from where I live.
“My son was up for the game but we didn’t go out. I never left the house.
“I couldn’t go out after what had happened and I ended up watching it over and over again.
“You have to understand the emotions of the city and I can’t talk about a different level of passion in Glasgow and not recognise or appreciate it.
“Can you imagine me being seen out for some pasta and a glass of wine? It wouldn’t have been right.”
Celtic exposed Rangers’ defensive frailties six weeks ago, but Warburton insists the scoreline flattered them and he defended his substitution – attacker Harry Forrester for injured centre back Rob Kiernan – when the score was 3-1 as he felt Rangers had to chase the game.
Within minutes, Phillipe Senderos was sent off, leaving Rangers even more vulnerable and Celtic rubbed salt into their wounds.
He said: “Would I have changed my opinion at 3-1 in terms of the attacking substitution? No, because I didn’t know then that we’d get a man sent off.
“Was it a 5-1 game? In my mind, absolutely not. The records will show that it was, but at 3-1 I still felt we could have nicked the next goal.
“We were playing against a very good team and there were other questions we had to ask ourselves.
“Was our intensity right? Did we play at the kind of level expected of us?
“Celtic were the better team on the day, I’m not arguing that. I still feel fine margins were involved and we need to show we’ve improved on Sunday.”
Warburton, who has Danny Wilson fighting to be fit, will certainly be ready for his BT Sport interview, insisting he has no dispute with the broadcaster despite not taking part in the usual, contractual pre and post-match interviews in Inverness last Friday night.
He said: “I had a couple of things I had to do. I did the media and I went back in. Suddenly it is that I have got a personal spat with BT Sport. I haven’t.
“I think I have always been good with BT Sport, always done the interviews before, always done the interviews after, always done what I had to do.
“Again, I look at these headlines with despair because they are looking for stories where there aren’t stories.”