Anelka dived to head home Florent Malouda's left-wing cross, 21 minutes from the end of a mundane and largely uneventful game on northern Portugal's wet and windy Atlantic coast.
With it, he secured Chelsea top spot in Group D but, perhaps more importantly, with a Barclays Premier League clash against Arsenal coming up on Sunday, ensured Carlo Ancelotti's team did not lose their impressive momentum in a game which ultimately mattered little.
Net buster: Nicolas Anelka slides in to extend Chelsea's lead at the top of Group D
This was an economical performance for the Premier League leaders,the sort which used to make Jose Mourinho glow with pride. There wasnone of the stylish football which has lit up much of Ancelotti's firstfew months at the club but it is a notable result against a Porto teamunbeaten at home since Manchester United's win in the Estadio Dragaolast season.
Further evidence of Chelsea's growing self-belief came in the shapeof a seventh clean sheet in eight games and the fact that theirunbeaten run away from home in Europe now stretches back more than ayear.
VIDEO: Ancelotti on Chelsea's win.
Ancelotti said: 'It is very important to keep momentum up, and wehave to keep this high moment. The players are in good condition and ingood form. We know Sunday will be a very difficult match but we alsoknow that we are in a very good moment to play Arsenal.
'It was our objective to finish first in this group. It is not easyto win here and the team did not play fantastic but just good. We tooksome risks in the first half, but the second half was much better andwe deserved to win.'
Boot room: Chelsea midfielder Michael Ballack feels the force of Raul Meireles' high-footed challenge
Ancelotti rested players with Sunday's trip to the Emirates in mind.Ashley and Joe Cole were among the substitutes, as were Michael Essienand Alex. There was a rare chance for Yuri Zhirkov at left back andreturns from injury for Michael Ballack and Didier Drogba.
There was a dreadfully slow early tempo and absence of urgencythroughout, with both teams already assured of a place in the last 16.It is debatable how beneficial top spot in the group actually is, butChelsea have never failed to reach the quarter-finals after winningtheir qualifying section.
On the two occasions they have finished as runners-up in the lastsix campaigns, they have been drawn against Barcelona and Juventus,winning one and losing the other.
In such an atmosphere, it took 15 minutes before either goalkeeperwas required to make a save. Anelka, scorer of the only goal when theteams met at Stamford Bridge in September, supplied the first test,cutting in from the left and having a go from 25 yards. Beto,deputising in goal for the injured Helton, made a meal of the shot andparried it unnecessarily.
Round the bend: Deco, playing against his former club, wraps a swerving shot around the advancing Alvaro Pereira
Porto were playing for the first time in 17 days after theinternational break and a postponement last weekend caused by awaterlogged pitch, and they surrendered lots of early midfieldpossession to their visitors.
LAMPS BACK ON TRACKFrank Lampard (right) may return against Arsenal on Sunday after a successful visit to massage therapist Marijana Kovacevic in Belgrade.
Lampard insists that he did not, however, undergo controversial placenta treatment on his torn thigh muscle.
Deco, one of five former Porto players in the Chelsea squad and,along with Ricardo Carvalho, one of two in the starting line-up, waswarmly applauded as he prepared to take a corner. He responded with alittle wave and boosted his popularity further by over-hitting theset-piece.
Going it alone: Ivorian striker Didier Drogba show his strength to escape the attention of FC Porto duo Alvaro Pereira and Raul Meireles
The Portuguese champions stirred midway through the first half.Fernando Belluschi was gifted the space to advance from midfield andunleash a shot which had Petr Cech stretching to his right. Cechblocked the effort and then reacted brilliantly to smother Falcao'sattempt on the rebound.
Five minutes later and Belluschi had Cech beaten. This time, theArgentine midfielder drifted in from the left and curled the ballbeyond the Chelsea goalkeeper with his right foot, only for it tostrike the bar and bounce to safety.
Enlarge Porto finished the first half on top, moving with more fluency andpassing the ball more crisply than Ancelotti's team, who looked utterlydisjointed in comparison to their slick performance against Wolves lastweekend.
Chelsea possessed greater adventure after the break. Deco fizzed a20-yarder narrowly wide and Malouda wriggled to the line on the lefttwice in quick succession before lashing low crosses into thegoalmouth. On both occasions, Malouda's good work was not matched by afinish.
Double act: Goalscorer Nicolas Anelka celebrates his winner with strike partner Didier Drogba
Deco continued to misfire spectacularly. Lining up an inswingingfree-kick from the Chelsea left, he sliced it horribly towards his owngoal and sparked a Porto counter attack, which ended with Cechgathering a centre at his near post from Raul Meireles.
Ancelotti threw up his arms in despair but soon the Chelsea manager was celebrating.
Anelka applied a finish to more excellent play from Malouda for hissixth goal of the season. His goals have won two games against Portoand one away to APOEL Nicosia.
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