A late header from Jesper Grønkjær gave FC København hope of progressing to the UEFA Champions League group stage after Steffen Iversen and Markus Henriksen had given Rosenborg BK what looked like being a useful two-goal cushion to take into their play-off second leg.
Iversen volleyed the home side in front on 23 minutes, putting the finishing touches to a flowing one-touch move which carved open the visitors' defence. Henriksen adroitly doubled the lead just before the hour with his third goal in this season's competition but Grønkjær's late intervention means FCK will still be in contention when the tie resumes next Wednesday.
Aside from Grønkjær's first-minute volley which cleared the crossbar it was Rosenborg who were the early aggressors. A move along the width of the FCK area ended with Anthony Annan shooting wide, before Iversen gave the home team the lead their early pressure had warranted by finishing off a move of the highest quality.
Rade Prica received possession on the edge of the area and flicked it on for Henriksen who in turn headed into the path of the waiting Iversen and the striker sumptuously fired in. The pace was befitting a Scandinavian derby yet FCK gradually regained their composure and twice came close to restoring parity before half-time through Dame N'Doye.
The forward came into the match having scored five times in his last three matches but showed none of that form when blazing over after Claudemir had sprung the offside trap and laid possession off on the edge of the area. A minute later Rosenborg goalkeeper Daniel Örlund kept the Norwegian league leaders in front, getting down sharply to his left to keep out N'Doye's low shot.
FCK were quickly onto the front foot after the break, too, almost profiting from a slip by Vadim Demidov which sent Grønkjær clear only for the winger to drag his shot wide. No sooner had they almost conceded, however, than Henriksen doubled Rosenborg's advantage on 57 minutes, providing the slightest of touches to divert Annan's drive into the bottom corner.
Having fashioned, and wasted, their chances, FCK could have fallen further behind had goalkeeper Johan Wiland not tipped over Iversen's strike before Thomas Kristensen cleared off his goal line following the striker's prodded effort moments later. Prica then slipped the ball against the post, a miss which was to prove pivotal as Grønkjær glanced in Hjalte Nørregaard's corner six minutes from time.