Andy Carroll's second-half header condemned the Blues to a fifth defeat in 10 matches as the ailing champions imploded at Upton Park.
Having seen Nemanja Matic red-carded on the stroke of half-time, and first-team coach Silvino Louro dismissed from the dugout, the embattled Blues boss did not emerge from the tunnel after the interval.
Mourinho, who already has a suspended stadium ban hanging over him for previous indiscretions this season, is now likely to find himself in hot water with the FA once more.
Meanwhile, on the pitch, Carroll's first goal since January ensured West Ham added Chelsea to Arsenal, Liverpool and Manchester City in their list of high-profile scalps this term
Mauro Zarate had fired the hosts into an early lead, and although t he 10 men of Chelsea responded admirably in the second half and levelled through Gary Cahill, substitute Carroll hammered another blow into their crumbling title defence
Chelsea did not look at the races in the first half - perhaps their midweek exertions in Kiev, from which Mourinho had named an unchanged side, had taken their toll.
Certainly Ramires and Diego Costa between them should have dealt with Dimitri Payet's near-post corner in the 17th minute
I nstead they made a complete mess of it and the ball flew across the box to Zarate, who had arrived just in time to drill it first time inside Asmir Begovic's near post
Chelsea were millimetres from equalising 10 minutes before the interval when Kurt Zouma's downward header was hacked clear by Manuel Lanzini on the goal-line
And their meltdown began in the 44th minute when Matic, already on a yellow card after fouling Zarate, cynically brought down Diafra Sakho to earn his marching orders
The Blues players surrounded referee Jonathan Moss in protest - which could also yield another FA charge - with the official eventually booking Fabregas and skipper John Terry.
Mourinho stood impassively on the touchline but, behind him, the incensed Louro's histrionics saw him removed from the dugout
Only when the Portuguese failed to retake his position pitchside, instead appearing in the stand amidst a flurry of camera phones - which no doubt would not have improved his mood - did word filter out that he too had been sent off.
Yet Chelsea managed to haul themselves level in the 56th minute after Zouma and Cahill challenged for Willian's corner, the ball falling kindly for the latter to thrash home.
However, Carroll had the final say, emerging from the bench to powerfully head in Aaron Cresswell's cross with 10 minutes left to inflict another damaging defeat on Mourinho and the Blues.
TWEET OF THE MATCH
"Andy Carroll....remember him? Well he's just put West Ham 2-1 ahead." - Gary Lineker on England striker Carroll's vital decisive goal.
Carl Jenkinson: 7
Aaron Cresswell: 7
James Tomkins: 7
James Collins: 7
Mark Noble: 7
Cheikhou Kouyate: 8
Mauro Zarate: 7
Dimitri Payet: 8
Manuel Lanzini: 8
Diafra Sakho: 7
Andy Carroll: 8
Pedro Obiang: 5
Angelo Ogbonna: 5
Asmir Begovic: 6 (out of 10)
Kurt Zouma: 6
Cesar Azpilicueta: 6
Gary Cahill: 5
John Terry: 5
Nemanja Matic: 4
Eden Hazard: 5
Diego Costa: 6
Cesc Fabregas: 5
John Obi Mikel: 6
Baba Rahman: 5
Dimitri Payet: Everything West Ham did well seemed to run through Payet
Honourable mentions go to Lanzini and Kouyate.
MOMENT OF THE MATCH
Nemanja Matic was sent-off for two bookable offences and Chelsea imploded
Silvino Louro, the assistant first-team coach, was sent to the stands and Jose Mourinho did not emerge on the touchline for the second half and was found sitting in the directors' box after he, too, had been sent off
It may yet result in a one-match stadium ban, although Mourinho is appealing the original sanction of a suspended ban.
VIEW FROM THE BENCH
West Ham made one enforced change, with Victor Moses prevented from playing against his parent club
Mauro Zarate came in to play a Chelsea side unchanged from Tuesday night's goalless draw at Dynamo Kiev
It was the first time this season Mourinho had named an unchanged starting XI
Numerically disadvantaged, Fabregas departed at the interval for Mikel, who brought a calm authority.
MOAN OF THE MATCH
Once again the focus of a Chelsea loss will be on referring decisions - Hawkeye denying Zouma a goal, Matic's bookings, the Fabregas strike which was ruled out for offside.
WHO'S UP NEXT
Watford v West Ham (Premier League, Saturday, October 31)
Stoke v Chelsea (Capital One Cup, Tuesday, October 27)
Source : PA