Stewart opened the overtime period with two free throws and hit a jumpshot to put Rider (2-3) up by three.
Following exchanged 3-pointers by both teams, Stewart nailed two more from the charity stripe to seal the win for the Broncos.
Myles was 7 of 13 from the field with a trio of 3-pointers and Zedric Sadler had 11 points.
The Owls (2-4) trailed by 12 late in the game, but Austin Ramljak sparked a run with two 3-pointers and a pair of free throws to tie the game at 80. They took a late 84-82 lead, but Stewart made a game-tying layup and Sean Obi's last-second missed basket sent the game to overtime.
Ramljak finished with 22 points and Seth Gearheart added 20, as both sank six 3-pointers.