Chelsea capitulated and were booed off as Southampton won at Stamford Bridge for the first time in almost 14 years to leave Jose Mourinho contemplating a fourth loss from eight Premier League games this season.
Captain John Terry was restored but Saints exposed the now familiar failings in the defence which just five months ago formed the foundation for winning the title.
Chelsea have conceded at least two goals in seven of their eight Premier League games this season – the exception the 2-0 defeat of Arsenal – and time and again Sadio Mane, Graziano Pelle and Dusan Tadic found holes in a 3-1 win.
Willian scored a fourth free-kick goal in four games to open the scoring, but Chelsea afterwards scarcely tested Maarten Stekelenburg as they fell to a first home loss to Saints since January 2002.
A rare Steven Davis goal levelled matters and Mane put the visitors ahead after mistakes by Gary Cahill and John Terry, before Pelle got Southampton's third.
Southampton might have had a penalty before the equaliser when Mane was tripped by Ramires.
The forward was soon after booked for diving, while Radamel Falcao received a yellow card for the same offence as Chelsea desperately sought something in attack.
Loic Remy was sent on after Pelle's goal, Nemanja Matic making way just 28 minutes after coming on as a half-time substitute.
But this was not a performance for one scapegoat as Chelsea disintegrated against an excellent Southampton.
Mourinho insisted there were no prima donnas or ostriches at Chelsea and his players accepted criticism, but Terry – making his second start in six games, the other at Walsall – might as well have had his head in the sand when a Tadic corner was floated over towards Jose Fonte.
Had the ball been a foot lower, it would have been 1-0 to Southampton as Fonte had lost Terry six yards out.
Oriol Romeu and Ryan Bertrand seemed keen to impress after being discarded by Mourinho, but both Southampton players were booked, the former for tripping Hazard's heels.
Willian curled the resulting free-kick into the far corner, but Saints – bar two tame Oscar shots – then went on the attack.
Ivanovic was unspotted in tugging back Virgil van Dijk before Davis sliced a good chance wide, and Ramires was fortunate not to concede a penalty for a trip on Mane.
The theatrical fall did not help Mane, who was moments later booked for diving after a tussle with Ivanovic outside of the box.
Fabregas was yellow-carded for diving in last December's fixture at St Mary's and Mourinho was furious there was no penalty award then.
Ronald Koeman had reason to feel aggrieved, but Saints continued to test Chelsea and Asmir Begovic had to be alert to claw away Victor Wanyama's cross and save from Bertrand.
Southampton equalised after Ramires was booked for a foul on Mane, and Fonte played the ball long to Pelle, with his back to goal.
Pelle held off Cahill, chested it and, one bounce later, Davis hit it sweetly to score.
Mourinho almost fell off his seat when Falcao was booked for diving and might have done so again when Cahill lost the ball and Terry failed to intercept Pelle's pass to Mane, who snuck in behind to slot in.
Mane ran at Chelsea and then played in Pelle for the third.
Chelsea tried in vain to find a response, but none was forthcoming in a second Premier League home loss in three games.
Mourinho had lost one of his previous 99.
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