Chelsea lost to Porto on Mourinho’s first return in 2004-05 and history repeated itself at Estadio do Dragao as Andre Andre and Maicon scored either side of Willian’s free-kick in the Group G clash.
Eden Hazard dropped to the substitutes bench alongside captain John Terry and Nemanja Matic as Mourinho proved there were no untouchables in his squad.
His hardline approach also followed his outspoken criticism of his players’ attitude, but Mourinho’s words did not have the desired effect as Chelsea looked vulnerable throughout.
Yacine Brahimi waltzed inside Branislav Ivanovic and behind Pedro, then fired in a shot which Asmir Begovic punched only as far as Andre, who hooked the ball in.
Willian replied with a delightful curling free-kick on the stroke of half-time, but then woeful defending allowed Maicon to head in a corner seven minutes into the second half.
Mourinho fumed: “We watch dozens and dozens of repetitions of Porto taking corners. We were completely ready for that and in a moment when the game is under control we concede a goal that is ridiculous.
“They hit the post from a similar mistake. Apart from that the game was balanced. Two ridiculous moments and we were punished.”
Diego Costa hit the bar, but Porto placed Chelsea under siege and the visitors were grateful to goalkeeper Asmir Begovic for some crucial interventions and a Danilo header came off the post.
Mourinho, who won the 2004 Champions League with Porto, was scathing in his criticism following Saturday’s 2-2 draw at Newcastle and 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.
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.
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.
Costa wanted a handball in the area against Marcano and Kenedy fired wide late on as Chelsea fell to defeat.
Casillas, Maxi Pereira, Maicon, Marcano, Martins Indi, Andre Andre (Layun 80), Danilo Pereira, Ruben Neves (Evandro 78), Imbula, Brahimi (Osvaldo 86), Aboubakar.
Begovic, Ivanovic, Cahill, Zouma, Azpilicueta, Mikel (Hazard 62), Fabregas, Ramires (Matic 73),Willian, Pedro (Kenedy 73), Costa.
Antonio Miguel Mateu Lahoz (Spain).