Nicolas Anelka stunned Porto for the second time this season as Chelsea finished top of Group D with a 1-0 victory in the Estadio do Dragao.
Anelka, who scored the winner when the two teams met at Stamford Bridge, stooped to head home a cross from Florent Malouda in the 69th minute.
It was another uninspiring performance from the Blues who had the woodwork to thank in the first half when Fernando Belluschi's 25-yard effort smashed off the crossbar.
But for the third time in Europe this season, Chelsea emerged winners by a solitary goal and in each of those games, Anelka has been the matchwinner.
Chelsea were quickly into their stride against Porto in a surprisingly sparsely populated stadium.
There were many empty seats among the Porto sections of the ground and the atmosphere which accompanied the start of the game was hardly intimidating for Chelsea.
In the sixth minute, Malouda, scorer of their wonderful opener against Wolves last Saturday, was off target with a 25-yard low drive which drifted wide of the target.
In the 15th minute, Chelsea won a corner when Didier Drogba's shot was turned over by Beto.
Unfortunately for the English side, Deco floated the flag-kick over everybody in the penalty area.
The Portugal international was given a warm reception by the Porto fans in that part of the ground.
In the 18th minute Michael Ballack almost finished off a neat move by the Blues but his final shot was deflected for another wasted corner.
But the home side almost took the lead in the 20th minute with their first real attack of the game.
Belluschi's 25-yard drive was palmed into the path of Radamel Falcao Garcia by Petr Cech but the Chelsea goalkeeper redeemed himself with another fine save at the feet of the Porto forward.
Porto were unlucky not to break the deadlock in the 29th minute when Argentinian Belluschi, playing his first game for a month, again tried his luck from 20-yards.
This time his shot beat Cech in the Chelsea goal but rebounded off the crossbar to safety.
Chelsea were living dangerously but Porto did not appear to have to guile to create anything other than the occasional long-range effort.
A 20-yard drive from Deco flashed past Beto's left-hand upright in the 36th minute.
It was hardly a thrilling spectacle and the stay-away Porto fans clearly made the right decision.
Jesualdo Ferreira's side may have come close to scoring with two long-range shots but Chelsea had coped easily with much of their attacking play.
Time and again Chelsea wasted the ball in good areas, with full-back Branislav Ivanovic one of the main culprits.
Chelsea had created nothing in an opening half that was instantly forgettable.
The English outfit had made a much better start to the second half and Deco sent a shot flashing beyond the far post in the 52nd minute.
Moments later, Malouda drilled two low crosses into the penalty area but they eluded the Chelsea strikers on each occasion.
At least there was more purpose about Chelsea's play now and Ballack was booked for a challenge on Cristian Rodriguez as the Porto player threatened to run clear.
Porto brought on the Hulk to great cheers from the home fans in the 59th minute. The Brazilian striker replaced Silvestre Varela.
In the 67th minute Chelsea replaced the ineffective Ballack with Michael Essien.
Essien, who scored two goals against Wolves last weekend, was left out of the starting line-up after collecting a minor knock on his knee.
But clearly coach Carlo Ancelotti was anxious to add some drive to a rather lack-lustre midfield.
It brought instant results, although not from Essien. Yuri Zhirkov broke down the left and his pass found Malouda inside the penalty area.
This time the winger's cross found the head of Anelka as the France international stooped to head his third goal of the Euro campaign in the 69th minute.
It was Anelka's sixth goal of the season and his first in eight games for the Blues.
In the 80th minute substitute Ernesto Farias brought a fine save from Cech with a low drive from the edge of the penalty area but Chelsea were home and dry.