IT may have been more perspiration than inspiration, but after another hard-fought encounter in the Highland capital Celtic moved seven points clear at the top of the Premiership.
And it was third time lucky for Ronny Deila after watching the Hoops lose and draw at the same stadium last season.
The sodden pitch didn’t prevent the lively Callum McGregor from giving the visitors the advantage in the eighth minute as he skipped through from the middle of the park.
As he demonstrated so capably against Ajax on Thursday, the youngster isn’t afraid to have a go from distance and he staged an action replay against the Highlanders.
McGregor, with the ball under his control throughout his foward run, timed his finishing effort to perfection and sent a measured drive low past keeper Owain Fon Williams down at his post.
It was a delightful goal from the winger who is certainly enjoying his return to the top side.
Celtic got a fright, though, in the 11th minute when Gary Warren was allowed the time and space to throw himself at a right-wing corner-kick. The ball crashed against Craig Gordon’s chest and bounced to safety.
Jozo Simunovic underlined he could be a threat, too, at set-pieces when he launched himself at a left-wing corner-kick. His long, looping, diagonal header swept dangerously just wide of the upright with Williams struggling.
Leigh Griffiths was keeping busy up front, chasing everything down with enthusiasm and purpose, Kieran Tierney was eager to add his weight to the attack with raids down the left, but Armstrong, despite working hard, was worryingly wasteful with his final pass.
He emphasised that when Simunovic, after some fancy footwork, stroked a ball out of defence and the former Dundee United midfielder inexplicably hit the ball straight to the surprised Greg Tansey who immediately set a counter-attack in motion.
Unfortunately, Armstrong wasn’t so fortunate in the 39th minute when John Hughes’ side equalised.
To be fair, the ball from Mikael Lustig was heavy, but Armstrong’s control let him down at the crucial moment and Liam Polworth seized upon the opportunity.
He slipped a ball through to dangerman Miles Storey, who too easily eluded Dedryck Boyata. Simunovic was too late with a sliding tackle and the on-loan Swindon striker’s shot was parried by Gordon.
Unluckily, it fell straight back to the frontman and, on this occasion, he couldn’t miss from an angle with the goal gaping in front of him.
It was yet another shocker from the Celtic defence and the sad story of a leaking back four who are finding it so difficult to keep a clean sheet these days.
Nir Bitton, with another of his wonderful long-range drives, thought he had netted a second just before the break, but his effort swept just wide of Williams’ left-hand upright with the keeper helpless.
There was no surprise when Allan made a welcome introduction in the 54th minute for the struggling Armstrong.
And, within five minutes, the former Hibs playmaker made an impact. He picked out the galloping Tierney on the left-wing and his first-timed cross from the bye-line was ideal for the lurking Griffiths.
The frontman didn’t hesitate as he hammered the ball wide of the exposed Williams from close range for his 19th strike of a prolific campaign.
Carlton Cole made his debut with half-an-hour still to play when he came on to play up front alongside Griffiths as Rogic made way.
And the former England international striker, released by West Ham in the summer, almost netted within four minutes after some trickery by McGregor on the right.
The winger teased and tormented the Caley defence before picking out Cole at the back post. The 6ft-plus hitman rose to head the ball down, but his judgement was just out and Williams managed to tip the ball over the bar on the rebound.
Stefan Johansen came to the rescue in the 76th minute when he had to hack a misguided clearance from Lustig off the line after a left-wing corner-kick had created danger.
It was all over in the 85th minute with a bizarre third goal. Allan was involved again with a neat pass across to Griffiths. He showed a trick or two as he cut inside to get the ball to his favoured left peg.
His blistering 20-yard drive was punched away by Williams at full stretch as Cole moved in for the kill. The ball struck the towering frontman, was deflected goalwards and took a final touch off Danny Devine before rolling slowly into the net.
It wasn’t a classic, but Celtic will take anything they can get from this ground. And it’s not often they can say they got a break against Caley Thistle.
TEAM: Gordon; Lustig, Boyata, Simunovic, Tierney; Johansen, Bitton; McGregor, Rogic (sub: Cole 60), Armstrong (sub: Allan 54); Griffiths.