Kevin Kelbie scored twice as Ballymena extended their unbeaten run to nine games with this convincing victory. The Scot shrugged off the challenge of a defender and slotted home the opener on 32 minutes and then turned in a Gareth Scates cross after 50 minutes.
Vincent Sweeney squandered a couple of chances before striking home the third in second half injury-time.
United had other chances while for Armagh, William McFrederick produced a fine save from David Hawthorne.
Conor Forker shot weakly into McFrederick's arms early in the game and David Ward fired over after the break.
Stuart King and Kelbie had other first half opportunities for the Sky Blues but poor City defending contributed to both of Tommy Wright's side's goals.