Liam Dunda scored the equalizer early in the third but the Owen Sound Attack couldn't get the puck past Charlie Graham in overtime and gave up a 2-1 decision to Hamilton.
Hamilton's Adam Laishram opened the scoring at 13:57 of the first. Neither team would score in the second period.
Laishram scored the winning goal in the extra frame.
Owen Sound's Michael McNiven stopped 18 shots, Graham blocked 27.
Owen Sound's Damir Sharipzyanov and Jonah Gadjovich assisted on Dunda's lone goal.