Former Celtic boss Neil Lennon admits he's a paid-up member to the Ange Postecoglou supporters club due to the Australian's efforts this season.
The 50-year-old Omonia Nicosia boss expected a response, after a season to forget that led to the Irishman walking away in February amid a botched attempt at 10 In A Row.
But even he has been left seriously impressed with the results and the style of play in which now play under Postecoglou's stewardship.
And now the current Celtic boss is eyeing a signature result at Ibrox.
Lennon believes it's Rangers boss Gio van Bronckhorst who now has some thinking to do ahead of the clash between the sides on Sunday.
Speaking on talkSPORT, he said: "I'm not surprised.
"We had a lot of problems last year and it wasn't a natural season.
"I make comparisons to Liverpool's season, when they had a lot of problems and just about made fourth place.
"I always thought Celtic would improved but he's done a marvellous job.
"He's really had to do a lot of surgery on the squad, which was required, but it seems to have been seamless.
"He had a really good January and I really like how Ange comes across in the media.
"I think he's pretty straight and I love the way that his team plays.
"The way that they handled the last Old Firm was fantastic.
"I don't think anyone seen that performance coming.
"For Gio (van Bronckhorst), he probably got the approach wrong and I think both teams will be firmly set on a huge encounter.
"The importance of this game will have ramifications as the season goes on."
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