The Grizzlies (10-9, 5-5 Big Sky) made 6 of 8 free throws in the final 64 seconds to hold off the Bobcats (10-11, 5-5).
Montana made 10 of its first 13 shots to open a 26-15 lead and shot 56 percent to lead 44-32 at the half. But the Grizzlies were ice cold as the second half started and the Bobcats clawed within 48-43.
Weisner made a layup at the 11:53 mark, ending a dry spell of 7:31 when the Griz missed nine straight shots and followed with 3. When the Cats got within one, he had five in a 7-0 surge.
Mario Dunn, Jr. added 13 and Jordan Gregory 11 for Montana.
Flavien Davis had 22 for MSU.