Gudjohnsen, starting for the first time this season in the absence of suspended Jimmy Floyd Hasselbaink, seized his chance with a goal in each half as Chelsea finally deflated their visitors.

Frank Lampard cemented the Blues' lead with a close-range finish in added on time to put Claudio Ranieri's men firmly in the ascendancy ahead of the return leg next Thursday.

Gudjohnsen rated his opening strike as one of his best ever - and Blues boss Claudio Ranieri, who last season saw Chelsea's UEFA Cup campaign end at the first round stage to St Gallen - was understandably fully appreciative.
 
The forward's neat, lofted finish in first half injury time came as Chelsea looked in danger of running out of attacking ideas.

For all their forward momentum, Ranieri's men had lacked precision in the final third from the off.

Boudewijn Zenden was in the thick of the early action. The Dutchman seemed to take an elbow to the face inside the box after five minutes, then was denied by a fine Georgi Petkov save.

From the ensuing corner William Gallas headed over when just five yards out, before Gudjohnsen scuffed a shot after neat build-up play by Lampard and the inspirational Gianfranco Zola.

The Blues's cause was hampered on 29 minutes when Emmanuel Petit, suffering from a chest infection, jogged off to be replaced by Jody Morris.

Ed de Goey did not have to make a save until the 42nd minute, when he fisted away Konstanti Golovskoj's dipping volley. Levski's best effort up to that point had been Biser Ivanov's second minute snap shot.

But with the half-time break imminent, Gudjohnsen changed the complexion of the game in an instant, skipping round three defenders before delicately lifting the ball into the net.

Chelsea dominated possession after the break, and Gudjohnsen and Zola could both have scored inside six minutes of the re-start. Jody Morris also had a strong penalty shout against Georgi Markov turned down.

Petkov once more thwarted a wasteful Chelsea front line with a finger-tip save from Zenden's header, but was badly out of position from the ensuing corner and Gudjohnsen gratefully took advantage by heading in.

Gudjohnsen had two half-chances for a European hat-trick, but the more pressing issue at stake was whether Chelsea could keep an important home clean sheet.

Stanimir Stoilov struck a left-foot shot just wide of de Goey's right hand post and Miodrag Pantelic swung in a late free-kick, but Chelsea survived before Lampard had the final say.