Chelsea's defensive frailties exposed again
Chelsea's struggles this season have been exacerbated by an uncharacteristically poor defence. They have now conceded 17 league goals - two more than they did in the whole of Mourinho's first season with the club in 2004-05.
Following Chelsea's defeat by Porto in the Champions League on Tuesday, fans called for the return of captain John Terry, and they got their wish on Saturday as the 34-year-old was restored to the centre of defence alongside Gary Cahill.
However, Terry's presence did not solve Chelsea's problems. Branislav Ivanovic and Ramires were fortunate to avoid giving away penalties with clumsy challenges, while Davis was allowed to run unchallenged to score the equaliser from Pelle's chested pass.
After the break, Cahill gave the ball away to Dusan Tadic and Terry failed to cut out his pass, enabling Mane to put Saints in front.
Mane was a constant menace to the Blues defence, which backed off to allow the forward to set up Pelle for Southampton's third.
With Diego Costa serving the last game of a three-match suspension, the visit of Southampton provided Radamel Falcao with a chance to make a case for a regular starting place.
He has scored only one goal since joining on loan from Monaco in July and, based on his showing against Southampton, it is unlikely he will be threatening Costa any time soon.
Although Falcao had a strong claim for a penalty when he fell under a challenge by Saints goalkeeper Maarten Stekelenburg, he did not trouble the visitors enough and managed a solitary shot in 90 minutes.