This was all about big-match temperament. Yet again, Billy Slater showed he's got it.

South Sydney didn't, and the result was the Rabbitohs were beaten 24-6 by Slater and an ultra-professional Melbourne in their NRL qualifying final.

As the Rabbitohs spent the opening 40 minutes mixing ill-disciplined penalties with obvious finals nerves in their first playoffs appearance in five years, Slater did what he does best - make the big stage his own.

His stunning 65-metre run in the opening few minutes - beating four defenders and another two with a slick pass - gave the Storm field position to score the first try.

Slater had a try of his own on 24 minutes, a hand in a third to Mahe Fonua before halftime and helped set up Sisa Waqa's four-pointer just after the break to make stew of the Rabbitohs.

While teammates Ryan Hoffman and Cameron Smith were probably the Storm's best over the 80 minutes, Slater's attacking spark proved vital.

Slater has missed much of the latter half of the season with a knee injury, which has needed careful management for him to take the field.

But any discomfort wasn't obvious once Slater was in his comfort zone - adding to a long list of big games for club, state and country for a player who once scored four tries in an NRL qualifying final.

Much was made of Slater's showdown with former teammate Greg Inglis in a battle of the game's star fullbacks.

Inglis showed glimpses from limited opportunities.

Slater's first half input turned the match, as the Storm moved to within one win of the grand final and the Rabbitohs failed their first finals test.

- AAP