Joe Rahon made 1 of 2 free throws with 6.6 seconds left to put Saint Mary's up 68-67. He then intentionally fouled Eric McClellan, thinking the Gaels had a foul to give. But McClellan missed the front end of a 1-and-1.
Fitzner hit two free throws with 2.9 seconds left and Gonzaga's Josh Perkins hit the front rim on a heave at the buzzer.
Saint Mary's went on a 14-3 run to take a 65-64 lead - its first advantage since 4-2. Rahon sank a 3-pointer and picked the pocket of Domantas Sabonis, which led to Fitzner's layup to cut Saint Mary's deficit to 64-63 with 3:34 left. Rahon hit a contested go-ahead layup with 2:45 left.
McClellan finished with 23 points for Gonzaga (14-5, 6-2), which led by as many as 15 points in the second half.