Nick Duncan added 15 points as the Broncos (3-0) overcame 33percent shooting. Drmic and Duncan each made four 3-pointers.
Martin Breunig scored 16 points, Jordan Gregory added 15 and Mario Dunn had 12 for the Grizzlies (1-1). Gregory made a tying 3-pointer with 5.3 seconds left in the second overtime but didn't get the shot off on time and was called for a shot-clock violation.
Drmic scored the tie-breaking basket on a layup with 1:55 left in the second session. He also converted a tying three-point play with 1:04 left in regulation and hit a tying 3-pointer with 19.5 seconds left in the first overtime.
The Grizzlies rattled off 14 straight points for an early 20-7 edge and their lead topped out at 25-10 on a 3-pointer by Jermaine Edmonds Jr. Montana led 30-20 at halftime.