Liverpool were on top from the first whistle put United held on to reach the interval 0-0.
But Jay Spearing (74 mins) and Craig Linfield (81) but the Reds 2-0 up before substitute Ray Putterill finished the scoring in injury time.
Peter Ramage made a return to action, starting the match but was substituted on 74 minutes.
There was no place for Olivier Bernard, who has been told he can leave the club in the summer.