Jose Mourinho suffered a miserable return to the home of one of his greatest triumphs as Chelsea's bad start to the season threatens to slide into a more serious decline.
What manager Mourinho had hoped was just a blip is becoming a worrying trend after bad defending and lacklustre individual performances once again cost Chelsea dear.
Mourinho tried to wake his Chelsea team from their slumber by making a raft of changes for his latest return to Porto, where he won the 2004 Champions League.
But while some of the Chelsea names may have been different in Portugal, much of the display was all-too familiar as goals from Andre Andre and Maicon were enough to earn Porto a happy 122nd anniversary.
Having complained about the "unstable attitudes" of some of his players, Mourinho dropped last season's Player of the Year Eden Hazard and midfielder Nemanja Matic to the substitutes' bench, while Oscar, Radamel Falcao and Loic Remy were left at home.
The decision raises doubts over the trio's future as Mourinho preferred to have no strikers on the bench with Diego Costa Chelsea's sole frontman. Mourinho's team selections had echoes of the dramatic decisions by Andre Villas-Boas and Roberto Di Matteo in the Champions League that effectively cost the duo their Chelsea jobs.
Villas-Boas was sacked shortly after dropping Ashley Cole, Michael Essien, Frank Lampard and Fernando Torres, and losing to Napoli, while Di Matteo was axed immediately after the defeat in Juventus, when he played Hazard up front instead of Torres.
Branislav Ivanovic somehow kept his place at right-back and captained Chelsea, but the defender's form showed no signs of improving and he was at fault for Porto's 39th minute opener.
Chelsea equalised with the last kick of the first half. Danilo fouled Ramires on the edge of his own penalty area and Willian gave Casillas no chance by planting the free-kick into the corner of the net.
Porto struck for what proved to be the winner in the 52nd minute thanks to sloppy Chelsea defending from a set-piece.
Ruben Neves delivered a corner to the front post and Maicon nipped away from Gary Cahill and in front of Ramires to head the ball into the net.
Afterwards, Mourinho blasted the team's defending.
"We watch dozens of repetitions of Porto taking corners. We were completely ready for that and in a moment where the game is completely under control and we were preparing a change, to concede that goal is ridiculous." (© Daily Telegraph, London)