The introduction of VAR to the competition saw Copenhagen dramatically awarded a penalty kick with 11 minutes remaining of a compelling first leg of the last 32 tie.
With the teams level at 1-1, Ryan Christie was sanctioned for a handball not immediately seen by the referee, collecting a booking in the process which means he will miss next week’s second leg at Celtic Park through suspension.
But the Scottish champions avoided a defeat which was have been extremely harsh on the balance of play when penalty specialist Forster saved Jens Stage’s spot kick.
A draw was the least Celtic deserved. They should have had more than Odsonne Edouard’s opener to show for their efforts, although Copenhagen improved after the break as they levelled through Dame N’Doye.
If the Copenhagen defence had been fully briefed beforehand on the potential danger posed by Edouard, they clearly didn’t pay sufficiently close attention.
They simply couldn’t cope with the pace, power and intelligent movement of Celtic’s top scorer as he ran them ragged from the opening exchanges.
Before he gave Neil Lennon’s side the early breakthrough their purposeful start fully merited, Edouard passed up a couple of arguably easier opportunities to score.
There were barely 20 seconds on the clock inside the smart and atmospheric Parken Stadium when he was presented with his first sight of goal. Christie, back in the starting line-up on the right side of the advanced midfield trio, surged forward and picked out Edouard’s run in behind the Copenhagen central defenders.
He looked the odds-on favourite in a one-on-one with goalkeeper Karl-Johan Johnsson but his shot was saved by the Swedish international before Victor Nelsson slid in to block the follow-up effort.
In the fourth minute, Copenhagen were cut open again. This time it was James Forrest, starting the evening on the left, who found Edouard. Again, he was denied by Johnsson who also reacted smartly to keep out Olivier Ntcham’s shot from the rebound.
There was a brief moment of concern for Celtic at the other end a minute later when N’Doye muscled his way into their penalty area but Kristoffer Ajer was able to do enough to prevent the Senegalese striker getting a clean shot away.
Celtic were soon back in control and it was no surprise when they fashioned another chance for Edouard in the 14th minute. It was a case of third time lucky for the Frenchman. His earlier misses had clearly done nothing to damage his confidence as he produced a sublime finish, dinking the ball over Johnsson from around 10 yards after Christie and Callum McGregor had linked up smartly to play him in.
Edouard looked poised to have another clear sight of goal four minutes later but this time a finely timed challenge in the penalty area by Copenhagen captain Carlos Zeca ensured the hosts did not fall further behind.
Stale Solbakken’s side gradually steadied the ship and while Celtic continued to dominate in terms of possession, there was some encouragement for the defiantly noisy home support when Bryan Oviedo got on the end of a sweeping move. The former Everton man might have done better than curl his shot wide of Forster’s left hand post.
The Celtic goalkeeper did not have a save to make in a highly satisfying first half for the visitors but he was beaten just seven minutes after the restart as Copenhagen began to perform with far greater intensity.and tempo.
Their reward was N’Doye’s equaliser which was nonetheless eminently preventable from Celtic’s perspective. Ntcham was punished for dallying needlessly in possession just outside his own penalty area, Copenhagen seizing the ball as Rasmus Falk threaded a pass to N’Doye inside the box. The veteran front man showed all his experience to guide home a composed finish via the inside of Forster’s right hand post.
Celtic’s response to the setback was positive and after Forrest, now on the right, saw a shot blocked, they wasted a promising opportunity to regain the lead when McGregor was guilty of unusually poor decision making when he blazed over from the edge of the box when he should have slipped the ball to the unmarked Edouard.
Yet another chance did come Edouard’s way in the 71st minute when he was picked out by Jonny Hayes’ low cross from the left but his first time shot from close range was brilliantly saved by the impressive Johnsson.
Celtic captain Scott Brown, booked for a cynical foul on Zeca, limped off injured and was replaced by Nir Bitton as an increasingly end-to-end contest entered the closing stages.
Just at it seemed the much hyped involvement of VAR would play no significant part in proceedings, Russian referee Sergei Karasev was invited to review the penalty claim for handball against Christie.
The spot-kick was duly awarded but Celtic were spared from a technology-aided defeat when Forster threw himself low to his right to touch Stage’s effort against a post before the ball was scrambled to safety.
COPENHAGEN: Johnsson, Varela, Nelsson, Sigurdsson (Papagiannopoulos 86), Oviedo (Bengtsson 73); Biel, Stage, Zeca, Falk; N’Doye, Santos (Kaufmann 73). Subs not used: Grytebust, Thomsen, Daramy, Bartolec.
CELTIC: Forster, Frimpong (Simunovic 83), Ajer, Jullien, Hayes; Brown (Bitton 73), McGregor; Christie. Ntcham (Elyounoussi 60), Forrest; Edouard. Subs not used: Bain, Bayo, Rogic, Bolingoli.