The former Molde attacker now has five goals at this level this term and his finishing prowess proved to be the difference between the two teams at a blustery Moss Lane.
The Cottagers carved out a couple of early chances with Courtney Harris heading over and danger-man Marcello Trotta forcing a diving stop out of Ben Amos. Although the Reds were on top, most of the nervous moments for visiting keeper Marcus Bettinelli were created by his own defenders, while Diouf could only fire off target after turning well on a header from fit-again Matty James.
After trialist Tom Naylor blazed across goal from a tight angle, the deadlock was broken at the other end when Dan Burn failed to deal with a long ball forward by captain Ezekiel Fryers and Diouf stole in before Bettinelli. Timing his finish to perfection, the Senegal striker waited for the ball to bounce before bravely looping a header into the net.
Substitute Davide Petrucci hammered off target from a Paul Pogba cross as United continued to call the shots but Federico Macheda picked up a yellow card for an off-the-ball incident with Joshua Pritchard. Burn headed a rare opportunity for Fulham wide before United looked to wrap up another victory.
Sean McGinty's header forced a great save out of Bettinelli and Reece Brown was denied from the rebound by a handball by the diving Ronnie Minkwitz on the line.
With no penalty forthcoming, the Reds kept probing and Marnick Vermijl was unlucky to see a prodded shot deflect inches wide following a solo run that took him past a couple of defenders.