Rosenborg 2 Celtic 0
Rosenborg striker Harald Brattbakk dealt a devastating blow to his former club Celtic's Champions League ambitions, scoring twice as the Scots crashed to defeat.
Brattbakk, who spent 18 months at Parkhead, scored both goals in the first half for the Norwegians to leave Martin O'Neill's side staring at a first phase exit from the competition in Group E.
Celtic now face Italy's Juventus in a must-win tie at home next week, although if Porto win at home against Rosenborg the Scots will be out.
Despite the defeat Celtic manager Martin O'Neill was upbeat about his "unlucky" side's performance.
"We've got beaten but thought we played very strongly indeed and were unlucky not to convert our chances," O'Neill told ITV.
"I thought the effort of all the players was terrific - I couldn't ask any more effort of them.
"To concede was disappointing considering we set out to try and get a foothold of the game - which I thought we were doing. It's a long way back from there."
Celtic looked out of sorts from the outset, striker Chris Sutton shanking an early right-foot effort well wide of the goal.
The Hoops had to do some desperate defending in the ninth minute after Bobo Balde's silly challenge on Brattbakk.
The former Parkhead forward then swung in a dangerous cross which Joos Valgaeren stretched to head behind for a corner.
Brattbakk could have hurt his former team-mates as early as the 17th minute after Balde failed to clear, but he snatched at the chance and blazed his volley wide from close range.
The Celtic fans must have felt that was typical of his career at Parkhead, where he was regularly barracked for frittering away scoring chances.
But Brattbakk wiped the smiles off their faces when he put the Norwegians in front in the 19th minute.
Janne Saarinen's long ball was headed down by Sigurd Rushfeldt and the Norwegian striker fired low and into the bottom corner from 25 yards.
Lively French winger Didier Agathe again got away from Saarinen in the 25th minute, but Celtic were unable to capitalise as Erik Hoftun made a vital tackle with Sutton waiting to pounce at the back post.
Nothing was going right for O'Neill's men and Stilian Petrov was booked for trying to stop Rosenborg from taking a quick free-kick after Johan Mjallby fouled Rushfeldt.
But it looked as though more goals would come and Robert Douglas had to save Roar Strand's stinging long-range shot at the second attempt after good work by Orjan Berg to tee him up.
Celtic, however, fell further behind in the 36th minute and it was Brattbakk again who made them pay.
Berg got away from Neil Lennon before passing to Rushfeldt whose shot was saved by Douglas, but the striker coolly took his time before picking his spot from 12 yards.
On the task facing his team next week, O'Neill added: "We know we have to beat Juventus.
"They're already through but I think Rosenborg are capable of getting a result in Porto.
"If we win the game it means Rosenborg will have to be beaten - but we'll give it everytyhing we have."
AFP