Conceding two more goals in the opening quarter of an hour failed to quench Valerenga's admirable spirit and, as five goals cascaded in on a wet Oslo night, a header by another famous Norwegian, Tore Andre Flo, was required to ensure a second Chelsea victory.
It was a welcome win after successive home defeats by Manchester United and West Ham had ended any triple crown ambitions, but it would probably be as well for the holders to avoid Lazio in today's semi-final draw.
It is the fourth time in their five seasons in the Cup-Winners' Cup that Chelsea have reached the last four and they need to rediscover the mixture of fluency and solidity evident earlier in this campaign to have a good chance of becoming the last winners of the competition.
Whether meeting Lazio, Real Mallorca or Lokomotiv Moscow next, they will surely need the guile of Gianfranco Zola (left on the substitutes' bench throughout) as well as a full-strength defence, rather than the patchwork combination on show last night.
Having failed to hush up injuries to Franck Leboeuf and Marcel Desailly, Chelsea's doctors of spin had more success with the right-back Albert Ferrer, who was unexpectedly named as a non-runner shortly before the off. Only Graeme Le Saux of the regular back four was in the side, while the young defender John Terry came in at right back.
Egil Olsen's choice was much more predictable, with Valerenga's record signing at pounds 600,000, the Swede Pascal Simpson, brought it as an extra attacker to partner the highly regarded John Carew, who underlined his potential and also his current weaknesses.
Both strikers might have embarrassed Chelsea in the opening few minutes following a series of dangerous thrusts. Simpson jabbed a good opportunity wide as Terry was left stranded between two home players, and Carew was sent clear, only to be let down by his first touch, the ball running on to a grateful Ed de Goey.
Suddenly, however, Chelsea had scored twice and the tie - if not the match - was determined. After 12 minutes Vialli's touch proved much sharper than Carew's as he controlled Terry's diagonal cross from the right for a tap-in. In their next significant attack his team won a corner, taken by Dennis Wise, which was headed out for Lambourde to drive in his first goal for the club.
With play flowing swiftly from end to end there were three more goals before half-time, the first and third of them to Valerenga. In the 27th minute their height advantage was finally put to good use at a set-piece as Olsen's troops crowded the six-yard box for a corner taken by Dag Riisnaes, which the centre-half Fredrik Kjolner headed in.
Kjolner, a prison guard, was then guilty of allowing Flo to escape his clutches at the other end and head home a cross by Dan Petrescu.
Incident piled upon incident, and four minutes from the interval the home side cut their arrears on the night to 3-2. Carew demonstrated his better qualities, outpacing the defence, heading a bouncing ball past De Goey and finishing from an acute angle as Chelsea looked in vain for an offside decision.
It had been a remarkable first half, featuring two defences as leaky as the roof of the press box, which became sodden as heavy rain fell during the interval. In the meantime Chelsea's assistant manager Graham Rix was making three substitutions: Andy Myers, Eddie Newton and Mark Nicholls all entering the fray.
The principle of giving squad players a run out was all very well, but it did nothing for Chelsea's cohesion, and maintained until the finish Valerenga's hopes of at least drawing the game.
They deserved an equaliser on more than one occasion. Tom Hovi received from Carew and forced De Goey to stretch his 6ft 4in frame fully in touching a weighted chip over the bar. Soon afterwards Carew's freekick from 25 yards was flying in until a deflection brought another corner.
Indiscipline continued to dog Chelsea's approach. Roberto di Matteo was fortunate that a goal did not result when he casually hit a clearance against Espen Haug, and Vialli, just back from suspension, might have received a yellow or even a red card after reacting stupidly to a challenge.
Valerenga (4-4-2): Kaven; Berntsen, Haraldsen, Kjolner, Tran; Walltin, Levernes, Hovi (Haug, 76), Riisnaes; Carew (Musaeus, 85), Simpson (Thorsen, 70). Substitutes not used: Bolthof (gk), Karlsen, Kaasa, Odegard.
Chelsea (4-4-2): De Goey; Terry, Duberry, Lambourde, Le Saux; Petrescu, Wise (Newton h-t), Di Matteo, Babayaro (Myers, h-t); Vialli, Flo (Nicholls, h-t). Substitutes not used: Hitchcock (gk), Percassi, Zola, Morris.
Referee: A Ancion (Belgium).Reuse content