Cronulla has staked its claim as a legitimate top-four team, plunging St George Illawarra's finals hopes into doubt with a 38-10 win over the Dragons.

In a result that has far-reaching ramifications for multiple sides, the Sharks ran in four unanswered tries on their arch-rivals in the final 25 minutes in Wollongong on Sunday.

The win moves the Sharks into third spot on the NRL standings, above Penrith on the ladder and only behind the Sydney Roosters on for-and-against.

The Dragons remain in eighth with must-win matches against Parramatta and Canberra to come, but still have four other finals hopefuls breathing down their neck.

It was only a few weeks ago that Cronulla's top-four credentials were being well and truly questioned, after an eight-game run where they won only two matches.

Since then they have claimed a scrappy 20-6 win over South Sydney, blown Gold Coast out of the water 44-0, and come back to beat Newcastle 19-18.

But Sunday's effort against the Dragons may have been the Sharks' best and most important win in months.

They started well, weathered the storm after halftime and eventually ran away with the game.

A win next Saturday night against the Warriors would all but ensure a top-four finish, ahead of their final-round clash with Manly at Brookvale.

And Cronulla will now enter that period as a team legitimately in form, with the only concern being a potential ban for centre Jesse Ramien after a high tackle.

Ramien had initially struck first for the Sharks, using his speed to step outside of opposite number Mat Feagai from a scrum.

Another first-half try came when Kayal Iro stepped Max Feagai after a Braydon Trindall cut-out ball, and Sam Stonestreet also stepped inside for another.

But it was a moment of magic from Will Kennedy that turned the match, after Ben Hunt's composure had got the Dragons back to 14-10 down after the break.

Kennedy swung the down when he leapt high over Tyrell Sloan to take a Trindall bomb and dot down under the posts.

Briton Nikora then ran through the Dragons' middle defence four minutes later, before Stonestreet and Mawene Hiroti both scored again as the hosts wilted.

Making matters worse for the Dragons, their for-and-against is now comfortably worse than Brisbane, the Dolphins and Newcastle below them.

And while their defence let them down late, it was missed opportunities in attack after halftime that proved most costly.

One try went begging when Sloan was found to have pushed a Shark off the ball before Zac Lomax crossed, and Mat Feagai threw another ball into touch on attack.

AAP