Dionte Christmas added 16 points for Temple (12-10, 5-3 Atlantic 10), which has won all three of its overtime games this season.
A 3-pointer by Forbes gave UMass a 64-61 lead with 3:18 left in regulation, but the Owls' Chris Clark hit a 3-pointer with 1:11 remaining, sending the game into overtime.
Another trey by Ryan Brooks gave Temple a 71-68 advantage with 2:50 left, and the Owls then converted 7 of 8 free throws to clinch the win.
For the game, the Owls made 22 of 24 from the foul line.
UMass is now 1-10 at Temple's Liacouras Center since the building opened in 1997.