Montana's Ahmaad Rorie tied the game at 77 with 30 seconds left. The Vandals ran down the clock before Blake drove the lane and his running jumper rimmed out, but Sherwood tapped in the ball to end the only regular season meeting between the teams.
Idaho (19-7, 11-3 Big Sky Conference), which beat the Grizzlies in last season's tournament quarterfinals, remains in third place in the conference standings behind Montana and Weber State (12-2). The Vandals travel to Weber State next Saturday.
Montana (20-7, 13-2) has lost two straight since having its 13-game winning streak snapped in a nine-point loss to Eastern Washington on Thursday.
Victor Sanders added 21 points for the Vandals. Sherwood finished with eight points and seven rebounds.
Rorie scored 21 points to lead four in double-figure scoring for Montana. Fabijan Krslovic made the first of two free-throw attempts for Montana to tie it at 71 with 46 seconds remaining in regulation. Jamar Akoh blocked Sherwood's jumper with 22 seconds left, but Rorie and Bobby Moorehead missed shots to force overtime.
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