An improved second-half display from the Premier League leaders was capped by Nicolas Anelka's 69th minute winner, though it was the home side who had the better of the openings throughout the 90 minutes.
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The goal came immediately after Michael Essien was introduced to the fray in place of Michael Ballack, who was cautioned ten minutes earlier.
The Ghana international picked up the ball midway through the Porto half and waited for reinforcements to arrive.
He quickly spotted £18million Russian Yuri Zhirkov, making a rare start at left-back, darting forward who in turn poked the ball on to in-form winger Florent Malouda.
Malouda's cross for French compatriot Anelka was pinpoint and the ball was emphatically headed home from point-blank range.
The goal was Chelsea's only attack of note in the match, as they were often pegged back by the pacy counter-attacking style from their Portuguese opponents, which could have put them out of sight in the first half.
Fernando Belluschi's drive from distance provided Chelsea keeper Petr Cech with plenty to think about in the couple of seconds the headguard-clad number one had before he sprang up to make it an impressive double stop as the onrushing Radamel Falcao thought that he had put his side a goal to the good in the 21st minute.
The long-range bombardment did not stop there. Ten minutes later, Belluschi almost produced one of the goals of the Champions League this season with a fearsome effort from 25 yards which dipped at the last moment to rattle the crossbar with Cech beaten.
Falcao and Cristian Sapunaru hit further shots from outside the area before the half-time whistle sounded, with Carlo Ancelotti's side clearly rattled.
The match was more of a contest after the break, with Deco going close from 20 yards, while a number of penalty claims from either side were ignored by Swedish referee Jonas Eriksson.
The introduction of the not-so aptly named Hulk galvanised the home side as they chased an equaliser, but the rearguard pairing of John Terry and Ricardo Carvalho never looked too uncomfortable as the Blues defended their lead.