San Diego (0-2) shot 50 from the field and made 6 of 11 from 3-point range in the first half to take a 34-28 lead into the break. But the Toreros fell cold in the second as the Broncos found their collective stroke.
After a 3-pointer by Duda Sanadze to open the second gave the Toreros a nine-point lead, they went six-plus minutes without a field goal. Western Michigan used a 13-1 run during that span to take a 41-38 lead and never trailed again.
San Diego made 10 of 30 field goals, including 3 of 17 3-pointers, after halftime.
Marcus Harris led San Diego with 13 points.