The Bulls fired a season-high 39 shots at Reign goalie Michael Hutchinson, but Chris Crane was the only S.F. player to score. Crane capitalized on a 5-on-3 power-play opportunity, 28 seconds into the third period.
Dan DaSilva, Cameron Burt and Adrian Van de Mosselaer scored for Ontario.
The Bulls return to action Wednesday for a road game at the Stockton Thunder.