The Ospreys (1-2) had tied the game with a layup from Dallas Moore with 34 seconds left. Moore finished with 18 points and five assists as UNF gave up a six-point lead with about three minutes to go. Chris Davenport added 17 points and four rebounds.
Northwestern (3-0) got 16 points and four assists from Bryant McIntosh; Demps came through with 15 points and five rebounds, and Sanjay Lumpkin chipped in with 13 points and six rebounds.
North Florida shot the ball well at 51 percent overall and had just 12 turnovers, but the Wildcats enjoyed a slight edge in three-pointers, going 10-of-23 overall.