The Sharks, sitting in 4th place, faced a surprising 22-16 defeat against the last-placed Dragons, reminiscent of last season's encounter.
Cronulla coach Craig Fitzgibbon noted a lapse in focus but remains optimistic that this loss will motivate his players as they aim for a top-four finish with four matches left.
In addition, the Sharks suffered a setback with star centre Jesse Ramien sidelined due to a pectoral injury, while also relinquishing the Monty Porter Memorial Cup to their rivals.
Nicho Hynes started strong, assisting Sione Katoa in the right corner with an impressive pass in the 5th minute.
However, Hynes missed a chance for his 33rd consecutive conversion, tying him with Nathan Cleary for the second-longest goal-kicking streak in NRL history.
Braydon Trindall made a critical defensive play against a Dragons' chip, and Hynes executed a solid tackle on Hamish Stewart to force a turnover.
St George ultimately scored, with former Sharks player Valentine Holmes capitalizing on a grubber and converting to give them a 6-4 lead.
Shortly after, Sharks fans believed they'd reclaimed the lead when Hynes broke through, but the referee ruled him held up.