Porto - 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 on Tuesday.
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.
Diego Costa was agonisingly close to a second goal for Chelsea when his wicked drive from 25 metres hit the underside of the bar and came out.
But Chelsea, who won the Premier League last season but are struggling sixth from bottom in their domestic championship this term, could have fallen further behind.
Porto laid siege to the visitors' goal in the last 20 minutes and Begovic had to be at his best to keep his team in the game.
Victory was especially sweet for Porto goalkeeper Iker Casillas who broke the Champions League appearance record by featuring in his 152nd game in the competition.
Porto have four points from two games in Group G while Chelsea have three.