Dutchman Koeman took charge of Valencia for the first time since replacing Quique Flores, but watched his side suffer a defeat which leaves their hopes of making the next round hanging by thread.

Iversen stunned the home crowd in the 31st minute when he controlled Marek Sapara's pass inside the area, turned and hit a low shot past Valencia keeper Timo Hildebrand.

Hildebrand, who stands in for injured guardian Santiago Canizares, was at fault for Rosenborg's second in the 58th minute.

He failed to handle a corner after mistiming his jump, allowing Iversen to head into an empty net and double the lead for the Norwegian outfit.

Elsewhere, Chelsea maintained their position on top of the group despite a goalless draw with Schalke

In the first-half, Ivan Rakitic and Heiko Westermann caused problems for Chelsea defense, who were missing inspirational defender John Terry due to injury.

At the other end, Schalke keeper Manuel Neuer twice denied Ivorian striker Didier Drogba in one-on-one situations.

Peter Lovenkrands could have snatched a precious victory for Schalke in the dying seconds of the game but his powerful shot was denied by the post.

Chelsea are in charge of the group with eight points, one ahead of second-placed Rosenborg.

Schalke lie third on four points while Valencia rooted to the bottom with three points.