Britt Assombalonga scored a first-half brace and his seventh goal of the season to continue Fulham's poor run of form.
The London club made the brighter start of the two sides, but it was a Henri Lansbury free kick from the right-hand side which helped Assombalonga nod in his first of the game at the near post to make it 1-0.
Forest doubled their lead and Fulham's misery after Michail Antonio was brought down in the box by Dan Burn to give Assombalonga the chance to double his goal tally from the spot.
Nottingham's new signing tucked the penalty away into the bottom left corner, with Gabor Kiraly guessing the right way but unable to get a hand to it.
Fulham gave themselves a chance to get back into the game thanks to a Ross McCormack free kick on the half-hour mark.
Hugo Rodallega had the chance to equalise after rounding Forest keeper Karl Darlow, but his shot was cleared off the line to keep the score 2-1 at half time.