Youssou Ndoye finished with 14 points on and pulled down 13 rebounds for the Bonnies (8-4, 1-0 Atlantic 10). Jaylen Adams also finished with 14 points for St. Bonaventure, while Andell Cumberbatch added 12 points.
Defense was the key for the Bonnies, holding the Minutemen to 35.2 percent shooting from the field and 4 of 21 from 3-point distance while forcing 15 total turnovers.
The game was close much of the first half, but Saint Bonaventure closed on a 7-0 run to take a nine point lead at halftime. UMass (7-7, 0-1) would trim the lead to three early in the second, but a 17-1 Bonnies run capped by a Cumberbatch layup put the game away.
Trey Davis and Dady Lalanne led the Minutemen with 12 points apiece.