The Lakehead Thunderwolves spent most of their game Saturday trailing the Waterloo Warriors.
But they spent the third period on even ground with their closest pursuer in the OUA West, then rode Mitch Fillman's second of the season at 3:34 of overtime to eke out a 3-2 win at Fort William Gardens.
Josh Schappert staked the Mustangs to a 2-0 lead, scoring at 16:03 of the first, then on the power play at 10:24 of the second.
The Wolves (15-3-0) would tie it up before the middle stanza ended.
Keith Grondin scored for the second time in as many nights to cut the lead in half, his power play goal coming with seven minutes to go in the period. Jake Carrick knotted the score with 1:01 left to play.
LU, who has opened a six-point cushion on Waterloo, hits the road next weekend for a date with the Ontario Tech Ridgebacks.