Jordan Coccimigilio opened the scoring at 5:29 in the first and Dylan McGuigan's shot at 14:09 gave the Bearcats a two-goal lead at the end of the first period in front of 1,501 hockey fans.
Halfway through the game, the score was tied at two thanks to shots from Jon Johannesson and Morgan Messenger.
Tyler Morrison scored the game winning goal less than a minute after Yarmouth's tying goal.
Travis Moore gave the Bearcats their fourth goal on a powerplay at 10:19 in the third.
Shayne Campbell stopped 32 of 34 shots for the Bearcats win.
Truro is looking to continue their winning record when they are home to the Metro Shipbuilders on Saturday. Game time is 7:30 p.m. at the Colchester Legion Stadium.