Peeved Gio van Bronckhorst admitted Rangers made “unthinkable” errors as Celtic delivered a brutal reality check by taking a huge step towards the title.
The champions’ 12-month reign is all but over after they failed to get a result that would have kept them in the Premiership flag race.
Aaron Ramsey looked to have finally delivered on his biggest outing in a blue jersey yet as he fired Gers ahead.
But his third-minute opener was quickly snuffed out by Tom Rogic before Cameron Carter-Vickers sealed a momentous win that moves the Hoops six points clear with six games to play.
Van Bronckhorst refused to throw the towel in but knows it will take a stunning Parkhead collapse to prevent the title crown from heading back to the East End of Glasgow.
“Well, losing today against Celtic made it more difficult for us,” said Rangers' Dutch gaffer.
“That is obvious. It is not over yet but of course the loss we had today makes it more difficult to be champion. If you play against your direct opponent for the race and you lose, you always make it more difficult.
“Our start couldn’t have been any better.
“The team started on the front foot and we scored an early goal, which is what you want.
“But the two goals we gave away were gifts.
“It cannot happen in any match - not only an Old Firm - but any match. You cannot give the first goal away like that.
“For me it’s unthinkable.
“But it happened and for the second goal as well we didn’t defend as strongly as we can.
“That’s why we conceded two easy goals against us. That made it more difficult.”
Rangers have had to wait two months to see Ramsey start a major match while the on-loan Juventus star battled to overcome a string of persistent fitness issues.
But while he looked energetic and sharp during the opening stages, his influence wained at the same time as Rogic took control for Postecoglou’s men.
Van Bronckhorst waited until 25 minutes to go before replacing Ramsey and Ryan Jack with Fashion Sakala and Scott Arfield but opted against using his three other permitted changes.
Defending his substitutions, the Ibrox boss also insisted he can shoulder the flak that will now come his way after seeing his side surrender their own six-point lead at the top.
He said: “Well I made my decision, that’s it.
“Of course it’s easy to talk about subs and why it didn’t happen. You bring in fresh legs. We put Sakala on the wing to get more bodies up front and to play with a lot of pressure up front.
“We created some chances to score. Not really big ones but enough chances to score the equaliser. If you lose, the subs are always bad. If you win, it’s always good.
“I’ve had both moments in this season so far. It’s the task of a coach and also if it doesn’t go well then it’s always the blame of the coach. I have tough skin.”
Rangers’ bottle crashed in more ways than one.
In scenes reminiscent of a Sunday League kick-about, the second half was held up by a few minutes as Ibrox groundstaff were called in to clear up shards of glass after a bottle was hurled towards Celtic keeper Joe Hart’s goal.
Blasting the culprit, van Bronckhorst said: “Of course it’s not what you want. You go out of the locker room and are preparing well for the second half, you want to go. Then you have to wait a couple of minutes.
“It’s never good that due to situations the game has to be stopped. I don’t think it’s a good thing.
“Safety is first and I understand we have to wait for the pitch to be playable for both teams.”
