(CNN) -- Nicolas Anelka stunned Porto for the second time this season as Chelsea finished top of Champions League 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 left-wing cross from Florent Malouda in the 69th minute.
But it was an 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.
However, for the third time in Europe this season, the English Premier League leaders emerged winners by a solitary goal and, in each of those games, Anelka has been the match-winner.
The result leaves Chelsea on 13 points and they cannot be caught, while Porto remain on nine points and go through to the last 16 as runners-up.
In the other match, Atletico Madrid remain a point ahead of APOEL Nicosia in the chase for a consolation Europa League spot as the pair drew 1-1 in Cyprus.
APOEL took a fifth minute lead when Nektarios Alexandrou crossed for Nenad Mirosavljevic to slot home at the near post.
But Atletico levelled in the 62nd minute when Simao Sabrosa found space in the left of the penalty area to fire home a low shot.
The draw was the Spaniards' third in five games, with their hosts just behind them on two points. Atletico entertain Porto in their final match and a win will secure them a Europe League place.
Meanwhile, 13 years after Fenerbahce became the first team to defeat Manchester United in a European game at Old Trafford, fellow-Turkish side Besiktas ended their 23-match unbeaten home record in the Champions League with a shock 1-0 Group B win.
Rodrigo Tello scored the only goal with a long-range strike in the 20th-minute, that took a slight deflection to deceive second-choice goalkeeper Ben Foster.
United, who had already qualified for the knockout stages, fielded a young side but they failed to get the point they needed to finish top of the group -- and still need a draw from their final match at German champions Wolfsburg.
Meanwhile, in the other group match, Wolfsburg missed the chance to book a place in the knockout stages as CSKA Moscow came from behind to beat them 2-1.
Wolfsburg had seven points from their four previous matches and a win at the Luzhniki Stadium would have booked their spot in the next stage of the competition.
However, after Edin Dzeko's opener for the Germans -- CSKA hit back through Tomas Necid and Milos Krasic after the break to keep their own hopes alive.
The visitors took a 19th minute lead when Obafemi Martins found space to slip in Dzeko, who timed his run perfectly to beat the offside flag and slot home from close range.
The equalizer came in the 58th minute and when Necid headed home after a clipped cross from the right by Eugeni Aldonin.
Krasic then secured the victory eight minutes later with a sublime 30-yard strike which powered into the roof of the net.
Both teams are now level on points, but Wolfsburg hold second place due to their 3-1 victory over CSKA earlier in the competition.
The Germans now know a win against United will send them through, while CSKA travel to Besiktas needing to better Wolfsburg's result.