The Vandals had tied it at 64 on Landon Tatum's short jumper with 25 seconds left.
Reggie Moore scored 15 points and Brock Motum added 12 as the Cougars (5-4) beat Idaho for the ninth straight time.
Idaho (4-4) was led by Stephen Madison, whose 18 points made him the only Idaho player in double digits. Deremy Geiger had four steals, and Idaho ended the game with 10 steals.
Idaho fought back from a 12-point deficit in the first half after shooting only 31 percent. The Vandals went 15 of 25 (60 percent) in the second half to help them come back.
HOOPS: Cougs win on last second jumper
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