Fitts made 12 of 20 from the field, including 4 of 8 from 3-point range, and grabbed eight rebounds for the Gaels (14-9, 5-3 West Coast Conference).
Tommy Kuhse, who added 17 points, split a pair of free throws to give Saint Mary's a four-point lead with 18 seconds left. Fitts capped the scoring with two foul shots with 10 seconds left.
Fitts' 3-pointer with 4:28 left in the game made it 77-62 for the Gaels. The Dons went on an 18-6 run to close the gap to 83-80 with 21 seconds left.
Saint Mary's took the lead for good at 5-4 and had its largest lead at 47-30 going into the break.
Michigan State's Rocket Watts (stress reaction) to miss Sunday's game
Michigan State freshman guard Rocket Watts is expected to miss Sunday's game against Rutgers with an injury.
Hauser carries Portland St. past CS Northridge 73-67
Matt Hauser had a career-high 29 points as Portland State defeated Cal State Northridge 73-67 on Friday night.
Elkaz leads UC Riverside over Cal Lutheran 74-40
Dragan Elkaz came off the bench to score 15 points and UC Riverside defeated Cal Lutheran 74-40 on Friday night.