Nicolas Anelka's second-half goal in Porto secured all three points for the Blues who now top their Champions League group.
Anelka stooped to nod home from two yards after excellent byline work from Florent Malouda.
The Blues have 13 points from five games in Group D and have one match remaining, at home to Apel Nicosia next Tuesday.
Before that Chelsea take on Arsenal at the Emirates Stadium and they have no fresh injury worries.
Didier Drogba, out for two weeks got a much-needed 90 minutes run-out tonight which will put him in he right frames of mind to face their north london rivals.
Joe cole had a useful 15 minutes while Yuri Zhirkov also continued his rehabilitation by playing the full match.
The Russian won't play on Sunday with Ashley Cole returning to left-back.