Chelsea completely lost their discipline as two sending offs, seven yellow cards and a penalty handed QPR a first win in this fixture for 16 years.
Jose Bosingwa and Didier Drogba both saw red, while Ashley Cole also picked up a suspension for his fifth booking of the season.
The rot set in when David Luiz needlessly conceded an eighth-minute penalty which Heidar Helguson scored, but the nine men wasted more than one chance to level, most notably when Nicolas Anelka headed straight at Paddy Kenny late on.
The defeat saw Chelsea blow the chance to capitalise on Manchester United’s derby humiliation and move second in the Premier League, while also leaving them six points adrift of Manchester City.
That merely added to the jubilation for the home fans as they celebrated their side’s first home victory since promotion.
Captain Joey Barton’s personal attack on opposite number John Terry six days earlier did not prevent the pair shaking hands before kick-off – but there was no love lost between the rival fans in what was a cracking atmosphere.
Daniel Sturridge and Luiz threatened early on but the latter’s habit of making daft challenges cost Chelsea dear in the eighth minute when they failed to deal with a long clearance and the defender nudged Helguson over in the box.
Foy pointed to the spot and Helguson snatched the ball from a far-from impressed Adel Taraabt and sent the penalty into the top corner via Petr Cech’s fingertips.
The were bossing possession without creating anything of note and their afternoon took another turn for the worse in the 32nd minute when Bosingwa was controversially sent off.
Bosingwa hauled down Shaun Wright-Phillips when the winger threatened to burst clear, with Foy deeming the right-back to be last man and brandishing red.
Chelsea were livid with the decision, which was followed by Taraabt curling the resultant free-kick too close to Cech.
Blues boss Andre Villas-Boas sacrificed Sturridge for Branislav Ivanovic but his misery was far from over, with Drogba getting himself sent off four minutes before half-time.
The striker lunged in two footed on Taraabt and – unlike his other two major decisions – left Foy with little option.
Villas-Boas took action again in first-half stoppage-time, withdrawing Mata for Nicolas Anelka.
It looked a lost cause for the nine men, who were sent out a full two minutes before their opponents after the break.
Incredibly, they went close to levelling straight away when Lampard was just beaten to Raul Meireles’ brilliant cross.
Kenny also flapped at a dangerous Ivanovic ball but they were soon hit on the break and John Obi Mikel was booked for upending Taraabt.
Lampard and Shaun Derry had to be dragged away from each other following a penalty-box scramble, with Foy booking both.
Luke Young screwed a great chance wide as Rangers finally began to make their advantage tell, while Ivanovic became the latest man cautioned for clattering Taraabt.
Barton picked up a customary yellow for going in late on Terry before Taraabt was withdrawn for Tommy Smith on the hour mark, the Moroccan also living up to his reputation for storming down the tunnel.
Young got in behind again five minutes later but he drilled his cross straight at Cech.
Lampard was furious midway through the half when he felt Fitz Hall had bundled him over in the box only to see the officials unmoved.
Luiz was booked for another poor challenge before seeing a penalty appeal turned down when he hit the deck under challenge from Helguson.
Barton almost scored on the break, and Meireles was booked for dissent before being immediately withdrawn for Florent Malouda.
But there was no stopping the yellow tide, Cole almost made to pay for his booking when Helguson volleyed over from point-blank range.
Chelsea should have capitalised with just over 10 minutes left when Ivanovic put the ball on a plate for Anelka, who somehow headed the ball straight at Kenny from four yards.
Jamie Mackie replaced Derry but Chelsea wasted another great chance to level when Lampard deflected Luiz’s overhead kick over the crossbar.
With time running out, Villas-Boas made his feelings clear to the fourth official, while tempers flared late on when Terry closed down Kenny and the pair squared up on the six-yard line.
There was still time for Cole to nod a weak header at Kenny and Cech – of all people – nearly to get his head on the end of a free-kick.