Hallam was 6 of 8 from the floor. Royce O'Neale chipped in eight points, six assists and five rebounds for the Pioneers (8-7, 4-1 Western Athletic), who closed the game on an 8-1 run.
Stephen Madison scored 19 points and Connor Hill had 12, including all three of his team's 3-pointers, for the Vandals (6-8, 2-2), playing their first WAC home game of the season.
Mike McChristian put Idaho ahead 48-47 on a layup with 1:35 to play, but Hallam's layup with 1:14 left gave Denver the lead back before Brett Olson, Cam Griffin and O'Neale each made two free throws to seal the victory.
Denver also won its only other games against Idaho, in 1965 and 1966.
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