Porto 2-1 Chelsea
Jose Mourinho suffered a nightmare homecoming as Porto, the club he led to the Champions League title in 2004, inflicted a 2-1 defeat on his woefully out-of-sorts Chelsea side in Group G.
Mourinho sprang a surprise before the game by leaving out Eden Hazard, Nemanja Matic and Oscar and the Londoners went behind after 39 minutes when Yacine Brahimi produced a surging run down the left and Andre Andre scored.
Brazil playmaker Willian equalised with the last move of the first half, curling a delightful free kick into the top corner of the net from 25 metres.
Porto then went back in front seven minutes after the break when Maicon stooped low at the near post to head a left-wing corner past keeper Asmir Begovic.
Mourinho was scathing in his criticism following Saturday's 2-2 draw at Newcastle, which left the defending champions 14th in the Premier League with two wins from seven games.
He appears no closer to finding the answers to Chelsea's poor form.
Costa returned up front after serving two games of a three-match domestic ban, but Hazard, Matic and Terry were substitutes and Loic Remy, Radamel Falcao and Oscar were not even selected to travel.
Mourinho once made a statement at Real Madrid by dropping Iker Casillas and a rotten relationship ensued.
The Blues boss issued a curt reply in relation to Casillas, now the Porto goalkeeper, on the eve of the match, saying he would greet him - probably in the frosty manner he met Arsene Wenger at Stamford Bridge 10 days ago.
Casillas seemed keen to prove a point on his record 152nd Champions League appearance and saved from Cesc Fabregas and then denied Pedro one on one. Pedro should have scored.
Sloppy Chelsea struggled to find any fluidity as Porto probed down Chelsea's right.
Ivanovic avoided punishment for a clumsy challenge on Vincent Aboubakar and, down Chelsea's left, Maxi Pereira shot across goal.
Brahimi next easily cut inside Ivanovic and evaded the back-tracking Pedro before firing a shot which Begovic could only palm out as far as Andre, who volleyed in.
Chelsea equalised after Ramires earned a soft free-kick. Willian curled in from 20 yards, with Casillas flat-footed.
Porto were ahead again with defending uncharacteristic of a Mourinho team, but becoming increasingly familiar this season.
Ruben Neves floated in a corner and Maicon got in front of Ramires, Gary Cahill and Costa to head in at the near post.
Costa beat Casillas with a fine effort which ricocheted off the bar before Hazard replaced John Obi Mikel and soon fired into the side-netting.
Porto piled on the pressure, with Begovic saving from Giannelli Imbula and then scrambling clear at the feet of Brahimi.
Ivanovic headed wide from a Willian corner, but Porto went closer when Danilo's header hit a post.
Costa wanted a handball in the area against Marcano and Kenedy fired wide late on after Costa made space as Chelsea fell to defeat.
