A lacklustre display away from home saw Chelsea deservedly beaten at Southampton on Saturday.
A slow start brought signs of what may follow, and Jay Rodriguez gave the home side the lead midway through the first half with a well-taken goal after tidy build-up play.
John Terry headed the Blues level within 10 minutes, but Southampton were immediately back in front when Rickie Lambert bent home a stunning long-range free-kick, and that was the way it would stay.
It rarely looked as though Chelsea would get going with the Saints the more threatening side for long periods, and only after the introduction of Eden Hazard on the hour did the balance of play tip in our favour.
The Belgian came close to an equaliser with a low cross-cum-shot and Victor Moses brought one excellent save from substitute goalkeeper Kelvin Davis, but Southampton held on to inflict a damaging defeat on a day when our main rivals in the Barclays Premier League all won.
Terry returned to captain the side at centre-back, with injured Gary Cahill missing out. Branislav Ivanovic was alongside the skipper.
Elsewhere there was no Juan Mata as Victor Moses, Oscar and Marko Marin started behind Fernando Torres up front. Eden Hazard was on the bench with Demba Ba.
Southampton made two changes from their 3-1 win over Liverpool. Adam Lallana and Gaston Ramirez missed out, with Steven Davis and Jason Puncheon their replacements.
A couple of early corners suggested the Blues would be quickly into their stride, but it was from one of these set-pieces that a Southampton breakaway brought the game's first chance. Jay Rodriguez picked up a loose ball inside his own half and after a sharp turn, ran at the heart of the Chelsea defence, finding space to shoot but doing so tamely straight at Petr Cech.
Two minutes later the Saints came forward again and Nathaniel Clyne should have done better when he hesitated inside the area, but Rickie Lambert still managed to get a shot away, Ivanovic closing it down quickly to prevent an opening goal.
There was no doubt which side was on top, with Chelsea struggling to find fluidity all over the field, and Southampton would go in front midway through the first half with a well-worked goal.
Petr Cech concedes against Southampton
Lambert did well to retain possession down their left flank, and fed Rodriguez inside. Direct once more, he strode forward and played a smart one-two with Davis, running beyond the Blues' static backline and finished calmly past Cech. There could be few complaints it had been deserved.
In the 10 minutes that followed Chelsea continued to struggle, but when a Moses cross was deflected behind it allowed Marin to send a corner over, and six yards from goal, Terry headed down and into the net for the leveller, but parity would last only two minutes.
John Terry scores against Southampton
John Mikel Obi fouled Lambert 30 yards from goal, and after a short delay, the striker lined up the free-kick and bent it perfectly into Cech's right-hand corner, beyond the goalkeeper's reach. It was a goal the striker warranted, having been a constant thorn in the Chelsea side for much of the first half.
Having just got back on level terms, the Blues had it all to do once more, but could barely get hold of the ball as Southampton passed it around the lush St Mary's pitch with purpose. In midfield former Chelsea trainee Jack Cork and Morgan Schneiderlin were getting the better of Mikel and Frank Lampard, who were too easily overrun when Davis dropped deep to become involved.
Southampton were forced into a change at the break with goalkeeper Artur Boruc forced off. His replacement was Kelvin Davis.
Cech was the first keeper in action at the beginning of the second period though, beating a cross-shot from Clyne behind at his near post.
Another Marin cross from the right, where he had taken a corner just before, bounced around the Saints area before falling to Lampard, whose snapshot was blocked by keeper Davis. The offside flag went up anyway, so any goal would not have counted.
Shortly afterwards the England man found space in the Southampton half to shoot, but instad fed Marin to his left. The German jinked inside to shoot on his favoured right foot, but Maya Yoshida blocked.
A quick Torres free-kick played in Cesar Azpilicueta down the right, and he pulled back for Moses, whose shot was deflected up over the goalkeeper towards the Southampton net, only for the 36-year-old stopper to get fingertips to the ball and knock it onto the bar and over.
Oscar tussles with Steven Davis
On the hour Rafael Benitez made his first change, introducing Hazard, twice a goalscorer on international duty for Belgium, in place of Marin. Moses switched to the left with the suboperating down the right with licence to roam.
Southampton were threatening less now but Rodriguez was allowed a free-header from a corner and should have done better than heading well wide from 10 yards, then the same player beat Ivanovic to a loose ball and brought a decent save from Cech. Chelsea's defence was unconvincing and lacking concentration, with Ryan Bertrand and Ivanovic once more caught napping by their hungry and dynamic opponents.
Hazard took a while to find his stride, but 13 minutes from time almost grabbed an equaliser after a burst into the Southampton area and shrugging off two challenges but his low drive flashed across the goalmouth and behind for a goal kick before Moses could arrive to tap home.
It marked the start of a late rally from the visitors, with Southampton pegged back inside their own half for the final 10 minutes, but only a Lampard free-kick, just over the bar, caused the home side any problems and so they hung on for what could be an important victory in their fight for survival. For Chelsea, Manchester United in the FA Cup on Monday just took on even more significance.
Southampton (4-2-3-1): Boruc (K Davis h-t), Clyne, Yoshida, Hooiveld, Shaw; Cork, Schneiderlin; Puncheon (Ward-Prowse 61), S Davis (Fox 84), Rodriguez; Lambert (c)
Unused subs Fonte, Ramírez, Forren, Do Prado.
Goals Rodriguez 23, Lambert 34
Booked Lambert 82, Schneiderlin 87
Chelsea (4-2-3-1): Cech; Azpilicueta, Ivanovic, Terry (c), Bertrand; Mikel (Ramires 71), Lampard; Moses, Oscar (Benayoun 75), Marin (Hazard 60); Torres.
Unused subs Turnbull, Cole, David Luiz, Ba.
Goals Terry 32
Booked Torres 75
Referee Jon Moss