It followed Toronto's rain-delayed 5-1 win in a game suspended from Wednesday night which umpires called in the top of the sixth inning with Toronto in front 2-1.
In the regularly scheduled contest, Overbay hit an RBI single in the top of the third and a sacrifice fly in the fifth.
Zaun's only hit was a two-run single in the sixth.
Two others had one RBI, including Marco Scutaro, who had three hits, and one run scored on a second inning wild pitch by losing pitcher Daniel Cabrera (6-6).
Adam Lind also had three hits for the Blue Jays, whose 13-hit attack led to the fourth win in their last five games.
Winner Roy Halladay (12-7) surrendered the earned run and seven hits in seven innings with a walk and seven strikeouts.
Baltimore's run scored on Luke Scott's sixth inning sacrifice fly.