The visitors started the second half strongly, having been under the cosh for much of the first 45 minutes, and they were on level terms after 54 minutes when Michael Tonge was tripped in the area by Michael Dawson and PETER NDLOVU converted the spot-kick.
But Forest regained the initiative as MARLON HAREWOOD netted his second goal of the game with a right-foot shot just three minutes later.
To make matters worse for Neil Warnock's side, they were reduced to 10 men when Chris Morgan was dismissed for violent conduct on the hour. That dismissal cost them dearly as ANDREW REID made the points safe for the home side after 71 minutes.
Forest had recovered from the early setback of losing striker David Johnson through injury to dominate the opening 45 minutes, and they deservedly took the lead.
They went ahead on the half-hour when HAREWOOD scored from the penalty spot after being up-ended by Robert Page.
Forest won a corner inside the opening three minutes of the first half, but Reid's flag-kick was cleared by Page.
Seconds later Matthieu Louis-Jean tried his luck, but his shot flew over the visitors' crossbar.
Forest continued to enjoy the better of the exchanges as United, who appeared rattled by Forest's early supremacy, regularly gave away free-kicks - and Danny Sonner let fly from 25 yards only to see his shot clear the crossbar.
Sonner then went close with a shot which was parried by visiting goalkeeper Paul Gerrard, who then had to save again from the lively Johnson.
But Johnson had to be replaced after 11 minutes by Gareth Taylor after sustaining an injury. Even so Forest made the pace of the game and still had plenty in reserve when the visitors did threaten a comeback.