Travis Binnion's youthful side gave a valiant effort, but the hosts proved too strong in a game that proved to be a steep learning curve for the Reds.
United trailed 1-0 going into at break, as a result of Ben Perry's opener, before Forest scored three in the second half to put the game to bed.
The Reds had the chance to score late on and grab a consolation, but Keehan Willows denied James Nolan from the spot to see out the clean sheet for the home side.
It was a bright start from Binnion’s side, who looked to get forward at every available opportunity in the opening stages of the game.