The Guelph Storm blitzed the Peterborough net in the first period and scored four goals on 22 shots.
Alexey Toropchenko, Keegan Stevenson, Liam Hawel and Isaac Ratcliffe all scored to give the Storm the early lead.
But it was Ratcliffe's 31st of the season that ended up being the winner.
Peterborough responded in the second period notching three goals but could not find the tying goal at any point afterward.
Ratcliffe put it away with an empty net goal with just 22 sec left in the third period.
It's Guelph's fourth win in five games.
