The Terriers had looked to be on course for a point after Jonas Lossl had saved Aboubakar Kamara’s 81st minute penalty.
But Fulham snatched all three points in a largely forgettable basement battle when Aleksandar Mitrovic broke the deadlock in the first minute of stoppage time.
Defeat means Huddersfield become the first Premier League side to lose seven times in the same month - eclipsing the half dozen losses suffered by Leicester City in April, 2001.
More importantly, this latest reverse leaves David Wagner’s men in danger of being cut adrift at the foot of the table.
Mitrovic’s winner came just seconds after Huddersfield’s own move had broken down deep in home territory when Erik Durm’s cross intended for Laurent Depoitre was cut out.
The ball was moved to Ryan Sessegnon and the youngster was soon tearing into the Town half before releasing Mitrovic, who beat Jonas Lossl in impressive fashion.
It meant a heart-breaking end to the afternoon for Lossl, who just ten minutes earlier had looked like being the hero for Town by saving Kamara’s penalty.
Chris Lowe’s blatant handball left referee Kevin Friend with no option but to point to the spot.
Mitrovic is the designated penalty taker for the Londoners but Kamara grabbed the ball and insisted he take it despite the pleas of club captain Tom Cairney and defender Calum Chambers.
Kamara, though, would not be swayed and this gave Town a lifeline with his penalty being poor.
That should have meant a point apiece from a poor game for two teams whose confidence seemed as low as their league standing.
The first half was a total non-event. Fulham goalkeeper Sergio Rico was almost left embarrassed by a 25-yard effort from Philip Billing that swervedly wickedly but otherwise neither side looked capable of making the breakthrough.
Alexsandar Mitrovic did have a couple of openings from corners but his headers went wide without troubling Jonas Lossl.
Matters improved markedly after the restart and Billing could have won it for Town with a late drive that flashed just wide.
Then came the ultimate sucker punch for Huddersfield, who are going to have all on to get out of trouble following this latest setback.