Gay sank a pair of 3-pointers to spark a 9-0 run that broke open a 36-36 tie midway through the second half. After that, the Aztecs (11-3) used a stifling defense that limited the Falcons (9-5) to just one field goal over the final 8:16.
Reserve Lorrenzo Wade had 12 points and 11 boards for the Aztecs, and Tim Shelton added 8 points and 11 boards.
Matt Holland was the only Falcons player in double digits with 17 points.
Grant Parker added 9 for Air Force, which fell to 6-23 in conference openers, including 4-6 in the Mountain West.