Celtic were left to regret missed opportunities from seven days earlier as they slumped to a painful first defeat of the decade and crashed unceremoniously out of the Europa League.

A last 32 tie which the Scottish champions should have had all sewn up had they taken their chances in Denmark last week was ripped from their grasp by a Copenhagen side who made the most of theirs at Celtic Park.

On a night when Neil Lennon’s team never really got going, they fell behind early in the second half to a Michael Santos goal. They looked to have at least forced extra-time when Odsonne Edouard levelled from a VAR-awarded penalty but then capitulated in the closing stages as strikes from Pep Biel and Dame N’Doye took Copenhagen into Friday’s last 16 draw.

Celtic players stand dejected after conceding to Copenhagen in the Europa League. Picture: SNS

Celtic may well go on to reaffirm their domestic dominance in Scotland over the next three months but for now, they are suffering the dismay of failing to join Old Firm rivals Rangers in the next phase of European competition.

As he had hinted on the eve of the match, Lennon’s reshuffle of his side in the absence of the suspended Ryan Christie and injured Olivier Ntcham saw Tom Rogic handed his first European starting appearance of the campaign.

A little more surprising, perhaps, was the inclusion of Mohamed Elyounoussi as the on-loan Southampton wide man continues to get back up to full speed following his recent lay-off.

But the Norwegian international was eager to vindicate Lennon’s faith in him and was prominent in most of Celtic’s best moments in a first half which generally saw them struggle to find any sustained fluency.

Elyounoussi’s first darting run of the evening off the left flank and into the Copenhagen penalty area in the ninth minute saw central defender Victor Nelsson alive to the danger as he made a smart block.

Six minutes later, a terrific cross from Elyounoussi was only partially cleared by Pierre Bengtsson. When the ball dropped to Kristoffer Ajer, his shot was blocked by Guillermo Varela.

It was scrappier than Celtic would have liked for lengthy spells and Ajer put himself under early pressure when he collected the first booking of the evening for a clumsy foul on Rasmus Falk.

Elyounoussi continued to catch the eye and he should have put Celtic ahead in the 22nd minute. Another fine run into the penalty area caused confusion in the Copenhagen defence as he looked to link up with James Forrest. A weak attempted clearance from Bengtsson saw the ball break invitingly back into the path of Elyounoussi but he blazed over with the goal at his mercy.

Copenhagen enjoyed periods of decent possession and carried menace on the counter attack. It needed an alert interception from Jozo Simunovic to deny Pep Biel a shooting chance inside the penalty area after slack play in midfield from the hosts.

The visitors were fortunate to survive a scramble of almost comical proportions inside their six yard box in the 31st minute. Greg Taylor’s cross saw Copenhagen goalkeeper Karl-Johan Johnsson make a fine save to spare Nelson from an own goal before Rogic’s effort from the rebound struck a post.

Celtic were finally building up a head of attacking steam as the interval approached and Edouard was unlucky to see his shot on the turn from Callum McGregor’s cross deflected wide off Nelsson.

Copenhagen were forced into a chance a minute before half-time when the pacy Mikkel Kaufmann limped off to be replaced by Santos.

The visitors’ goal enjoyed two lucky escapes in first half stoppage time, first of all when Elyounoussi failed to force the ball home from a tight angle after Johnsson had flapped at a deflected shot from Edouard, then when the French striker was unable to get enough power on a close range header which the ‘keeper comfortably saved.

Celtic were left to rue those missed opportunities when Copenhagen stunned the home support by taking the lead six minutes into the second half.

The goal was a calamity for Simunovic who was woefully slack and short with an attempted pass back to goalkeeper Fraser Forster. The loose ball was pounced upon by Santos who surged into the penalty area from the right. He tried to pick out strike partner Dame N’Doye with a low cross but when the ball broke back to him off Christopher Jullien, he displayed good awareness to loft a shot over Forster into the roof of the net from around 10 yards.

Celtic were rattled by the setback and increasingly ragged for a period after it when Copenhagen appeared capable of increasing their advantage.

Lennon switched to three at the back in a bid to regain the initiative but Copenhagen continued to look assured. The Celtic boss made his first substitution of the night with 20 minutes remaining, the tiring Elyounoussi making way for Leigh Griffiths.

The striker was given a rousing reception from the home support as he joined Edouard up front and he almost made an immediate impact, sniffing out a chance amid a frantic goalmouth scramble and seeing his shot brilliantly saved by Johnsson.

Celtic were running out of both ideas and time but were thrown a lifeline by Copenhagen defender Ragnar Sigurdsson whose handball as he blocked an Edouard cross saw VAR invoked and a penalty awarded with seven minutes remaining.

Edouard was coolness personified as he dinked the spot kick beyond Johnsson to relight the atmosphere inside Celtic Park once more.

But it was almost instantly doused when Copenhagen regained the lead just two minutes later. More loose play from Celtic allowed Rasmus Falk to set Pep Biel free in the box and he slotted a low shot under the advancing Forster.

Crestfallen Celtic now needed to score twice to win the tie but they were put out of their misery when Copenhagen added a third of their own in the 88th minute, N’Doye waltzing through the middle to beat Forster with ease.

Celtic 1-3 Copenhagen (2-4 agg): Second-half collapse at Parkhead sees Celtic out