Chelsea's miserable 2015-16 season continued as they fell to a stunning 3-1 defeat against a rampant Southampton side at Stamford Bridge on Saturday.
The hosts took the lead through Willian's free-kick, but Steven Davis deservedly levelled proceedings just before half-time.
Chelsea thought they should have had a penalty when Radamel Falcao was brought down by Maarten Stekelenburg in the second half shortly before Sadio Mane put the Saints in front after a mistake from the returning John Terry. Graziano Pelle then sealed a victory which piles further pressure on manager Jose Mourinho.
The champions have now taken just eight points from as many matches after conceding three times in a home league game for the first time ever under the Portuguese boss, while Southampton have won three consecutive games and scored 12 goals in the process.
Mourinho had said before the match he would continue to rotate his side as he searches for a winning formula and he did exactly that with four changes as Falcao, Eden Hazard, Oscar and captain Terry were selected. Former Blues midfielder Oriol Romeu started in place of James Ward-Prowse in the only alteration made by Ronald Koeman.
Chelsea took the lead in the 10th minute after Romeu had been booked for a foul on Hazard out wide.
Willian stepped up and his 30-yard delivery found the far corner after bouncing off the post. It was unclear if the attempt was deliberate, but the Brazilian celebrated scoring for the fourth game in a row.
Virgil van Dijk's penalty appeal was turned down after Branislav Ivanovic had a hold on his shirt at a corner, before Davis lashed an effort wide as Southampton attempted to respond.
At the other end, Stekelenburg saved Oscar's curling effort after the playmaker had combined well with Cesc Fabregas in a tightly-congested penalty area.
The Saints were appealing for a spot-kick again when Mane went down in the box but their appeals were denied by referee Robert Madley despite contact being made during Ramires' challenge.
Southampton were the better side as the first half drew to a close and great work from Mane saw him dribble infield and send through a pinpoint pass for Ryan Bertrand, but Asmir Begovic narrowed the angle and denied the defender a goal against his former club.
The equaliser did arrive one minute before half-time though. A long pass from defence was chested down far too easily by Pelle on the edge of the box and Davis stepped up to rifle a low shot into the bottom corner.
Both sides made changes at the break, with Nemanja Matic replacing Ramires and Ward-Prowse coming on for Romeu.
Within minutes of the re-start, a sweeping Southampton passing move almost resulted in a goal, but Begovic did well to repel Mane's effort at close-range following Dusan Tadic's square pass.
Chelsea were struggling to generate clear-cut opportunities but felt they should have had a penalty. Falcao outmuscled Jose Fonte and went down in the box as he attempted to round Stekelenburg, but received a booking for what the referee saw as a dive.
That decision proved costly for the champions on the hour-mark. After Gary Cahill had given away possession, Pelle slipped through a pass which Terry completely misjudged, allowing Mane to race through on goal. Begovic got something on the ball in his attempt to save but not enough to prevent his side falling behind.
There was more woe for Chelsea on 72 minutes. This time it was Hazard who gave away the ball and Mane led a swift counter-attack before setting up Pelle to convert with a lethal finish into the far corner.
A crucial block from Terry denied Southampton a fourth after Mane won a battle of strength against Cahill down the left and brilliantly set up Tadic.
Chelsea almost had a goal back when a poor piece of goalkeeping from Stekelenburg allowed substitute Pedro the opportunity to shoot, but the ex-Barcelona man was just off target.