The Sky Bet Championship leaders arrived at Craven Cottage unbeaten in seven matches, but were undone by a Fulham side previously without a win in six thanks to goals from Nikolay Bodurov and Cauley Woodrow.
In a lacklustre display, it took the Rams over an hour to register an effort on target against a team who they had put 10 goals past in their previous two meetings this season.
Former Fulham loanee Darren Bent fired an early shot wide for the Rams, but the hosts dominated the rest of the first half and had a two-goal lead at the break which they never looked like relinquishing.
Ross McCormack and Ryan Tunnicliffe flashed shots wide, Shaun Hutchinson headed over and Lee Grant made a good save after Scott Parker’s drive flicked off the head of Woodrow before Fulham made the breakthrough in the 31st minute.
Bryan Ruiz skipped past Tom Ince on the left-hand side of the Derby area and when the Costa Rica forward’s shot was blocked by Cyrus Christie, the ball looped up towards Bodurov on the corner of the six-yard box.
The Bulgarian centre-half, not renowned for his finishing, had only stayed upfield following a corner but he expertly guided the ball over Grant with the outside of his right boot for his first goal since joining Fulham last summer.
And on the stroke of half-time Woodrow, only in the starting line-up because of an injury to Hugo Rodallega, doubled Fulham’s lead.
Parker won the ball in midfield and scampered forward before laying the ball off to McCormack, who chipped in an inviting cross for the onrushing Woodrow to nod in at the far post.
Derby had come from two goals down to thrash Fulham 5-2 in the Capital One Cup in October but there was no sign a of a repeat performance, especially after Bent limped off holding his hamstring.
Ryan Shotton headed an early chance wide while Ince’s deflected shot finally gave Marcus Bettinelli something to do, before the Fulham keeper kept out a Jeff Hendrick header at the far post.
But it was Fulham, who were starting to look anxiously over their shoulders at the relegation battle following their recent poor run, who came closest to scoring again.
McCormack was denied by a last-ditch block by Craig Forsyth and a point-blank save from Grant before sub Moussa Dembele crashed a shot against the crossbar late on.