Huberdeau was left all alone in the slot, and he fired a wrist shot into the top corner of the Attack net past goaltender Jordan Binnington. The victory clinched a spot in Sunday's final for the Sea Dogs, no matter what happens in their game Tuesday night against the Kootenay Ice (7 p.m., Rogers Sportsnet).
Tomas Jurco tied the game with 3:27 left in the third, as the Sea Dogs overcame a 2-0 first period deficit to set up the comeback win in a wild, back-and-forth overtime.
Stanislav Galiev had Saint John's first goal, and goaltender Jacob DeSerres made 47 saves to earn the win.
Matt Petgrave and Andrew Shaw replied for Owen Sound. Binnington made 41 saves in a losing cause in net in front of a largely pro-Attack capacity crowd at the Hershey Centre in Mississauga.
The Sea Dogs are now 2-0-0 after opening the tournament Friday with a 4-3 win over the host Mississauga St. Michael's Majors, who face Owen Sound on Wednesday night to close out the round-robin.