Dwayne Polee II drained a 3-pointer with 4 seconds left to give the Aztecs an improbable come-from-behind 67-65 victory that extended their winning streak to 19 games.
Xavier Thames finished with 23 points for San Diego State (20-1, 9-0 Mountain West), who trailed by 14 points in the second half.
Close is the typical result when the Aztecs and Broncos (15-8, 5-5) play. The past six meetings between the schools have been decided by six or fewer points.
Mikey Thompson led the Broncos with 16 points and Thomas Bropleh and Derrick Marks both added 15.