Myles was 7 of 12 from the field and had nine rebounds. Myles was 3 of 4 from 3-point range.
Jonathon Thompson scored 18 and Nurideen Lindsey added 10 for the Broncos (3-3).
Rider led 34-26 at halftime, only trailing early in the first half.
Glenn Powell led Jacksonville (2-4) with 22 points and 12 rebounds. Keith McDougald had 20 and Jarvis Haywood added 12.