The Ducks rounded off their pre-season campaign with a 7th win out of 7 friendlies.
Larry Burrell put the Gingerbreads ahead on 31 minutes, before United equalised through Paul Ward's own goal on 42 minutes.
Dennis Jenas put the visitors back in front in the second half before Steve Cox levelled from the spot after Glenville Donegal had been brought down.
Owen Wright put United in front for the first time when he converted Allan Pluckrose's cross before Donegal put the result beyond doubt at 4-2 in the 80th minute.
