Champions-elect Chelsea were expected to walk it against their relegation-threatened neighbours but instead they suffered a miserable defeat that left manager Jose Mourinho fuming.
He was so upset with the display that he used all his substitutes within 45 minutes but battling Fulham, who scored the winner after 16 minutes, still held Chelsea at bay to claim a memorable win.
The result was a major boost for manager Coleman, whose job was said to be on the line in the build-up to the game.
But he got his tactics right against a Chelsea side who racked up 16 corners to none in reply and had a goal disallowed for handball - but still ended the game with nothing.
Mark Pembridge and Steed Malbranque were outstanding for Fulham, while goalkeeper Mark Crossley made a stunning late save to deny John Terry an equaliser.
There was also an injury-time flare up when frustrated Chelsea lost their rag and had Gallas sent off for stamping on Heidar Helguson. But the story ought to belong to Fulham.
In a remarkable first half the Cottagers completely turned the formbook on its head and left Mourinho with a face like thunder.
They should have been ahead after only seven minutes when Terry crudely brought down Moritz Volz as he surged into the area. But astonishingly referee Mike Dean refused to give a penalty.
Lacklustre Chelsea didn't heed the warning signs and allowed Malbranque and Michael Brown to rush them out of their stride in midfield.
Collins John headed wide from a Boa Morte cross after 15 minutes but the hosts took the lead seconds later.
The lively Malbranque slid through a pass for Boa Morte in the centre of the box and, under a challenge from Paulo Ferreira, the Portuguese winger cannoned it into the net.
Mourinho was so furious with his team's display that he hauled off Joe Cole and Shaun Wright-Phillips after only 25 minutes and brought on Didier Drogba and Damien Duff in their place.
It briefly made a difference as Duff saw a left-foot shot superbly turned away by Crossley before Frank Lampard's follow-up effort was blocked on the line.
Fulham had a glorious chance to double their lead when Pembridge sent John through on goal - but Petr Cech denied him with a fine save.
Robert Huth also produced a stunning block to deny John, while Pembridge thumped a 49th-minute free-kick against the woodwork.
Mourinho, clearly upset at his team's display, dumped Huth at half-time in favour of Ricardo Carvalho, but although Chelsea forced plenty of corners they didn't match Fulham's intensity.
There was a moment of real controversy after 59 minutes when Drogba took advantage of a long ball that caught Boa Morte and Crossley napping.
But although he spun away to score into an empty net, the home players surrounded referee Dean claiming Drogba had controlled the ball with his hand.
There was confusion as Chelsea celebrated and Fulham argued - until the referee consulted his assistant and disallowed the goal.
Video replays showed Drogba had certainly used his hand to bring the ball down, and Chelsea had to try again.
They pummelled the Fulham goal, taking their corner tally to 16 without reply, and saw Boa Morte head one effort off the line and a Drogba effort deflect onto the crossbar.
Lampard fired a glorious chance over the bar after 70 minutes, but Fulham hung on in glorious style to score a famous victory.