Slavisa Jokanovic’s charges deservedly led at the break thanks to Tom Cairney, who opened the scoring in spectacular fashion 15 minutes in.
They all but put the outcome beyond doubt before the hour-mark, teenage left-back Ryan Sessegnon producing two confident finishes from largely identical positions.
After taking their time to recover, the Magpies pulled one back through substitute Daryl Murphy, but – in truth – a grandstand finale never looked likely to materialise.
Fulham could even have added to their lead at the death, only for Tim Ream to fire wide from the penalty spot.
Despite a first defeat since January 2, Newcastle still sit top of the table, though their lead over third-placed Huddersfield Town has been cut to six points.
The Cottagers made the more purposeful start, enjoying plenty of the ball early on.
Ten minutes in, Sone Aluko produced a smart turn midway inside the Magpies’ half, and rolled the ball into Cairney, who skied his effort from 25 yards.
It didn’t take long for Cairney to make a more meaningful impact, however.
On the quarter-of-an-hour mark, Stefan Johansen picked out Scott Malone down the left, whose centre was gathered by Cairney. The former Blackburn Rovers midfielder took a touch to set himself, before superbly finding the net from range.
After Newcastle failed to make anything come of a corner from the left, the Cottagers broke quickly through the middle. Goalscorer Cairney threaded the ball through for Aluko, who checked inside before bringing a decent save out of Karl Darlow.
Fulham continued to look by far the brighter side, and with 20 minutes on the clock, Neeskens Kebano saw a right-footed strike bobble wide via the leg of Paul Dummett, Cairney again the architect.
It took almost half an hour for United to create a truly meaningful chance, as Vurnon Anita’s inviting cross was met by Ciaran Clark six yards out, who saw a goalbound header tipped over by David Button.
That was as close as the Magpies came prior to the interval, however, as a disappointing first half came to an end.
Far worse was to come after the break, though.
Barely five minutes in, Johansen was afforded room down the left flank, and the Norwegian’s low-struck cross was misjudged by Dummett. The ball bounced into the path of Aluko, who teed up Sessegnon to coolly slot home.
The Magpies almost responded through Dwight Gayle, who saw a looping header kept out by Button after Matt Ritchie’s cross from the left took a deflection.
Again, the hosts failed to threaten from the resultant corner, and they were caught on the counter in devastating fashion.
Aluko advanced into the United half and slid the ball through for 16-year-old Sessegnon, who got the better of Darlow with time to pick his spot.
With less than an hour on the clock, it looked like a hammer blow for Newcastle, who offered little in the following exchanges,
75 minutes had gone before they next mustered an attempt of note, substitute Jesus Gamez skewing wide of the near post from 20 yards.
Seconds later, however, they did generate a flicker of hope.
Christian Atsu’s lofted ball forward was well-judged by Murphy, who stepped back inside before bending into the far corner from the edge of the penalty area.
Unfortunately, it was to prove little more than a consolation, as the visitors gave little away in the closing stages.
The scoreline could have been more emphatic had Ream converted from 12 yards, Dummett having given the spot-kick away following a foul on Sessegnon.
The American fired wide of Darlow’s left-hand post, though it was to matter little in the end, as the Cottagers comfortably saw out the remaining four minutes of stoppage time.
