Darren Fletcher’s side stormed into a four-goal lead inside the first 45 minutes, thanks to braces from Louie Bradbury and Jay McEvoy.
After the break, the home side threw everything at United, with Charlie Blackshields scoring and Rio Parmer netting a double but the Reds held on to win and move into the semi-finals.
Gabriel and West Brom’s Harry French were both sent off for straight red cards.
FIRST HALF - REDS HIT FOUR
United started the better of the two teams and nearly opened the scoring when Godwill Kukonki met Bendito Mantato’s cross, but his strike outside the area went just over.