Entering the third period, No. 17 Union looked like it was going to be upset by Notre Dame in the first round of the fifth annual Shillelagh Tournament.
However, Matt Wilkins tied the game with only 1:45 left in the third period with a power-play goal, and followed that by scoring the overtime game-winner with 22 seconds left in the OT.
In the process, the Dutchmen avenged their loss to Notre Dame the last time they played, ironically also in the Shillelagh Tournament in 2009.
Notre Dame took a 1-0 lead on a goal by Sam Herr on a backhand shot at 7:34 of the first. Austin Wuthrich made it 2-0 when he deflected a Luke Ripley slap shot at 14:31 of the second period.
Union started its rally when Spencer Foo scored on a wrist shot from the left faceoff dot at 8:04 of the third period.
Union will face Western Michigan (which defeated Ohio State earlier in the day) in the championship game of the Shillelagh Tournament Saturday at 4:05 p.m. Union has won its last 11 games against Hockey East opponents dating to December 2012.