Allegheny (1-0) started the scoring with a goal from Tom Ludwig in the 34th minute.
Mount Union (0-1) tied the game at 1-1 just under two minutes later when T.J. Welch (Columbia Station/Columbia) knocked in a penalty kick.
The game would remain tied 1-1 at halftime.
D.J. Egan then leaped over two Purple Raiders and headed in a throw-in from Adam Spisak for a spectacular goal that turned out to be the game-winner in the 70th minute.
Spisak would feed Egan again with a cross six minutes later that resulted in the 3-1 final.
Mount Union is back in action Friday against Waynesburg (PA) College at the Geneva College Tournament in Beaver Falls, PA.