Rob Ferguson added 19 points, including 5-for-5 shooting from 3-point range, for Saint Joseph's, which defeated the Owls for the fifth straight time and 12th time in 13 games.
Dionte Christmas scored 24 points and Mark Tyndale 18 for the Owls (9-9, 2-2), who had their three-game winning streak snapped. Tyndale, who scored Temple's last 10 points, hit a driving layup with 41 seconds left to give the Owls a 67-65 lead.
But Tyndale missed the first of a 1-and-1 opportunity with 16.8 seconds left, and Calathes then made his game-winner from deep on the right wing.
Tyndale's difficult runner at the buzzer was tipped by Ahmad Nivins, and Temple hoped for a goaltending call. The referees ruled the shot was still on the way up.
Temple hit on three straight 3-pointers, including two by Christmas, to take the biggest lead of the game, 29-18, with 5:27 left in the first half, but Saint Joseph's responded with a 10-2 spurt.
The Owls, led by Semaj Inge's 12 points, held a 35-28 edge at the half.
Inge was playing for starting point guard Luis Guzman, out with a hip injury, while the Hawks were missing point guard Tasheed Carr, sidelined with a sprained right ankle.
