Match ends, CFR Cluj 2, Celtic 0.
A much-changed Celtic side slipped to their first defeat in seven Europa League games this season, losing 2-0 to CFR Cluj in Romania.
Neil Lennon, whose team had already clinched top spot in the group and will be seeded for Monday's last-32 draw, made nine changes to the side that beat Rangers in Sunday's League Cup final.
And second-half goals by Andrei Burca and Damjan Djokovic ended the Scottish Premiership side's 12-game winning run in all competitions and gave Cluj a second win over Celtic this term.
Lennon - who left several first-team regulars in Glasgow - gave a debut to 18-year-old Scott Robertson, while 16-year-old Karamoko Dembele became the youngest player to represent Celtic in Europe.
Celtic's B team struggle in Transylvania
With top spot and qualification for the last 32 assured, Lennon opted for a team that lacked game time and, in some cases, experience too. And on a cold winter night, they struggled to impose themselves on a Cluj side that knew a victory would see them accompany Celtic into the knockout stages.
The first warning of a Romanian threat came from Billel Omrani. The Algerian forward scored twice and provided an assist at Celtic Park four months ago when Cluj knocked Lennon's side out of the Champions League and looked certain to score again in the 17th minute in Transylvania.
After latching on to a cut-back from Lacina Traore, Omrani had the entire Celtic goal beckoning but was unable to curl the ball beyond an on-rushing Craig Gordon.
Celtic tried to turn the momentum but with a tentative midfield duo of Olivier Ntcham and Robertson, they struggled to dominate possession in the way they had in their previous group games.
Traore then came close with a header shortly after the half hour when he latched on to a cross from Ciprian Deac, while a right-footed shot from Mihai Bordeianu five minutes from the break looked destined for the back of the net before it ricocheted off a Celtic player.
What the first half hinted at, the second half delivered. Cluj finally broke through three minutes after the break when Burca pulled away from Boli Bolingoli to latch on to a corner and head in at the front post.
Just three minutes later, the Romanians almost doubled their lead when a left-footed shot by Deac forced a superb save from Gordon.
Celtic showed some intent through a Leigh Griffiths header and a Mikey Johnston shot either side of the hour, before Ntcham's right-footed shot from outside the box forced a save from Giedrius Arlauskis.
Yet Cluj continued their search for a second goal. Twenty minutes after missing his own close-range opportunity, Deac latched on to a cross and cut the ball back to an unmarked Djokovic, who scored from inside the six-yard box.
Celtic responded by bringing on Vakoun Bayo, a fringe striker returning from injury, and 16-year-old Dembele, while regular starter James Forrest remained on the bench.
At full-time, the home support celebrated watching their side qualify from the group stages for the first time. But for Celtic, it is a game that they and their fans will surely forget soon enough.
Man of the match - Ciprian Deac
Deac is by no means a spring chicken at 33, but the Cluj winger did more than enough to put Celtic to the sword after setting up both of his team's goals.
In a match that offered very little in terms of attacking intent, Deac was instrumental in breaking the deadlock and proved to be a vital player as his side made history.
- Celtic have failed to score for the first time in Europe this season in what was their 14th game. They last drew blank in both last-32 matches against Valencia last term.
- At 16 years and 293 days old, Dembele is the youngest player to play for Celtic in major European competition.
- Cluj have qualified for the knockout stages - and won three successive home games - in a European competition for the first time.
- Ciprian Deac has been directly involved in five of their Europa League goals, scoring two and providing the assist for each of the last three.
- 45Malino PaulinoBooked at 68mins
- 10DeacSubstituted forHobanat 85'minutes
- 8DjokovicSubstituted forCoimbra Aurélioat 83'minutes
- 9OmraniSubstituted forGolofcaat 74'minutes
- 1Fernández Collado
- 6Coimbra Aurélio
- 2JullienSubstituted forAjerat 45'minutes
- 16MorganSubstituted forBayoat 67'minutes
- 19JohnstonSubstituted forDembeleat 72'minutes
- 9GriffithsBooked at 71mins
- Halis Özkahya
- Shots on Target
Second Half ends, CFR Cluj 2, Celtic 0.
Foul by Moritz Bauer (Celtic).
Lacina Traoré (CFR Cluj) wins a free kick in the defensive half.
Attempt saved. Lacina Traoré (CFR Cluj) left footed shot from the left side of the box is saved in the centre of the goal. Assisted by Mihai Bordeianu.
Attempt blocked. Mihai Bordeianu (CFR Cluj) left footed shot from the right side of the box is blocked. Assisted by Ovidiu Hoban.
Corner, CFR Cluj. Conceded by Moritz Bauer.
Substitution, CFR Cluj. Ovidiu Hoban replaces Ciprian Deac.
Substitution, CFR Cluj. Luís Aurélio replaces Damjan Djokovic.
Offside, CFR Cluj. Mihai Bordeianu tries a through ball, but Catalin Golofca is caught offside.
Attempt missed. Olivier Ntcham (Celtic) right footed shot from outside the box misses to the left.
Attempt saved. Ciprian Deac (CFR Cluj) left footed shot from the left side of the box is saved in the top centre of the goal. Assisted by Juan Emmanuel Culio.
Karamoko Dembele (Celtic) wins a free kick in the attacking half.
Foul by Juan Emmanuel Culio (CFR Cluj).
Corner, CFR Cluj. Conceded by Karamoko Dembele.
Substitution, CFR Cluj. Catalin Golofca replaces Abdel Billel Omrani.
Substitution, Celtic. Karamoko Dembele replaces Michael Johnston.
Corner, Celtic. Conceded by Andrei Burca.
Leigh Griffiths (Celtic) is shown the yellow card for a bad foul.
Goal! CFR Cluj 2, Celtic 0. Damjan Djokovic (CFR Cluj) left footed shot from very close range to the high centre of the goal. Assisted by Ciprian Deac.