Goals either side of half-time from Gary Liggett and Ryan Harpur proved enough to give the Swifts their first win of the season over Ballymena.
Liggett shot home at the far post in the 32nd minute after Matt Hazley's mis-hit effort had fallen to him.
Soon after, Harpur's quickly-taken free-kick was saved by Macauley Cairns.
Harpur ran onto David McCullough's through ball and smashed home from the edge of the box on 68, then Neal Gawley scored direct from a corner late on.
With next week's Irish Cup semi-final against Queen's University in mind, United manager Glenn Ferguson made 11 changes to his starting line-up from last week's win over Glenavon.
The result moves Darren Murphy's side to within four points of seventh-placed Ballymena.