Reynolds showed what else he had in his kit bag, grubbering for Dylan Farrell to double the lead.
But Cronulla stuck to the task and came up with a reply via Michael Gordon, who picked up a bouncing ball after Todd Carney had beaten three defenders in a run near the line.
Reynolds added a penalty goal after the halftime siren.
The Sharks lost Luke Lewis to injury 12 minutes into the second half, and the Rabbitohs looked like they had kicked away via Nathan Merritt before the hour mark only for the try to be denied because of obstruction.
Ryan's try added to the Rabbitohs' frustration as did another no-try video referee ruling. South Sydney 14 (A Everingham, D Farrell tries; A Reynolds 3 goals) bt Cronulla 12 (M Gordon, B Ryan tries; M Gordon 2 goals).
-AAP