With Reece Walsh outpointing Latrell Mitchell in the battle of the superstar fullbacks, the Broncos stormed home in the second half after the Rabbitohs had equalled the scores at 12-12 in the 45th minute.
Walsh and rookie winger Deine Mariner scored two tries apiece, while left centre Selwyn Cobbo, in just his second match since moving from the wing, was too hard to handle for the Souths defence.
However, the win was dampened by an injury to Reynolds, who started the match with his right knee heavily strapped and was forced from the field in the 70th minute.