Sonny Bill Williams and Anthony Tupou are potential game-breakers in the NRL grand final, but Craig Fitzgibbon says beware their fellow bench players.

New Zealand international Williams and possible Kangaroo bolter Tupou have been the shock weapons during the finals series for the Bulldogs and Sydney Roosters respectively.

They shape as the super subs in Sunday's decider at Telstra Stadium following what's expected to be a torrid opening quarter.

There's no doubting their talent and ability, but Fitzgibbon says other reserves can also pack a mighty punch.

"I think it's the underrated guys who are slipping under the radar," said Fitzgibbon.

"I know Corey Hughes probably changed the game for the Bulldogs the other night and the same with Reni Maitua's try (in the preliminary final win over Penrith).

"Sonny Bill had a blinder and Roy Asotasi carried the ball well.

"The four bench players were the ones who turned the game and yet for us, we've got very underrated players who come on.

"We certainly lose nothing when we make an interchange.

"Those players don't get the raps they deserve, particularly blokes like Chad (Robinson) and Neddy (Catic)."

Brought to you by AAP © 2024 AAP