Cronulla took advantage of an error-riddled St George Illawarra to run up a 10-0 halftime lead in Monday night's NRL local derby at a rain-soaked Toyota Stadium.

Showing far greater tenacity and cohesion than they displayed in their first-up loss to Canberra last weekend, the Sharks bullied the premiers into a spate of dropped balls with some rugged defence.

After opening the scoring through a Ben Pomeroy try on 14 minutes, Cronulla's endeavour was rewarded on the stroke of halftime when Anthony Tupou crashed over to leave the premiership favourites staring down the barrel.

The Dragons were their own worst enemy with Brett Morris, Matt Cooper and Ben Hornby all losing possession inside the Sharks' red zone, the home side let off the hook following a run of early penalties.

A John Morris bomb was tapped back by John Williams before Pomeroy touched down with his second grab at the ball, but the Dragons looked like coming back when they earned three straight sets at the Cronulla line.

A Jamie Soward 40-20 gave them another opportunity which Brett Morris wasted when he stepped on the sideline as he dived over, and the Sharks were seemingly happy to settle for a 4-0 lead at the break.

A penalty against the Dragons with ten seconds remaining looked like pushing it out to a six-point lead, only for fullback Nathan Gardner to take a quick tap.

His tactic looked like it had backfired when he was tackled, but a quick play the ball saw Albert Kelly put Tupou over next to the posts.

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