Chelsea were indebted to another superb goal from Eidur Gudjohnsen as Claudio Ranieri's side eased into the second round last night.
The Icelandic striker, who scored twice against the Bulgarians last week, delivered again after John Terry swept in his first goal of the season to end all resistance.
Levski Sofia had a new man in charge since last week's first leg - their third coach in a fortnight. Nasko Sirakov was replaced by Georgi Todorov, who made three changes to the team who lost at Stamford Bridge. Among the casualties was the captain Stanimir Stoilov.
On a slippery pitch, Gianfranco Zola won a corner after only 40 seconds as he almost got the better of Stanislav Angelov. Then Terry slipped in his own area as he tried to cut out a cross, but he recovered to concede a corner.
Mario Melchiot conceded a free-kick just outside his area after 15 minutes for a foul on Rogero Botelho, but the Dutch defender did well with a headed clearance when the ball was swung into the box.
Chelsea had a golden chance of an away goal after 26 minutes. Following a corner, Melchiot backheeled into the area. It fell perfectly for Terry, but the defender shot straight at the goalkeeper from 15 yards.
Terry soon made amends, but not before a double scare for Chelsea. Georgi Chilikov was denied by Emmanuel Petit's block and then by William Gallas' diving header.
After 29 minutes Gudjohnsen had a shot diverted for a corner. Then, as Petit's eventual deep cross from the right was nodded down by Melchiot, Terry drove home.
The goal silenced the home crowd and had Chelsea's 350 fans celebrating, knowing the tie was effectively out of the Bulgarians' reach.
Petit might have scored after 39 minutes but lost control in the six-yard box. But again Chelsea's disappointment was short-lived. In first-half injury-time, Gudjohnsen delivered a brilliant solo effort. Supplied by Gallas, the Icelandic striker twisted and turned past two defenders before firing high into the net.
Gudjohnsen was given a rest after 54 minutes, being replaced by Mikael Forssell. Then Ranieri brought off Zola and sent on the England Under-18 striker Leon Knight for his Chelsea debut. Within two minutes he sent in a teasing cross which just eluded Forssell.
There were ironic cheers from the home fans as Dimitar Telkiiski had a low shot on target from 25 yards which was comfortably saved by Ed de Goey after 65 minutes.
Levski Sofia: Petkov; Stankov, B Ivanov, Markov, Angelov, Telkiiski, Botelho, Topuzakov, Golovskoj, Pantelic (Stoilov, h-t), Chilikov (Genchev, 71min).
Chelsea: De Goey; Melchiot, Terry, Desailly, Gallas, Babayaro; Lampard, Petit, Jokanovic (Dalla Bona, h-t); Zola (Knight, 59), Gudjohnsen (Forssell, 54).
Referee: M Ingvarsson (Sweden).
