The NRL can dream of a crowd of more than 50,000 at Stadium Australia next week, after Manly blew their shot at a home final with a 40-20 loss to Cronulla.

Needing a win to claim hosting rights for next Saturday's elimination final against Canterbury, Manly fell to their biggest defeat of the year.

They were left wanting defensively either side of halftime, and desperately missed injured fullback Tom Trbojevic in attack ahead of his anticipated return next week.

Cronulla, in contrast, were as polished as they have been in a long time after slipping behind 8-6 early.

Already locked into fourth spot and a trip to Melbourne for their qualifying final, the Sharks grew more confident in attack as the game went on.

The result made them only the second team to beat Manly at Brookvale this year, with Braydon Trindall again producing the goods in the halves.

Had Manly won, it is likely a week-long debate would have ensued around venue requirements for finals given the 17,400 capacity at 4 Pines Park.

Instead, it's anticipated a crowd of more than 50,000 could attend Accor Stadium on Saturday night, which would mark the highest of the NRL era for a first-week final in Sydney.

Canterbury and Manly drew 35,502 fans for the less-than-desirable Friday 6pm timeslot last week, and far more would be expected for a knockout final.

Manly beat the Bulldogs last week, but have won only three of their past 17 matches at the venue, dating back to the 2013 grand final.

And while Canterbury have slipped up in the final fortnight, Manly will need to be much improved on how they played on Sunday to survive beyond next week.

The Sea Eagles had success out wide early and a damaging Haumole Olakau'atu run briefly put them back in the game in the second half.

But otherwise Manly were well below their best as they let in the most points they have all year.

The Sea Eagles finished the game with 41 missed tackles, as Cronulla cut them open through the middle and on the edges.

The Sharks' first try came in easy fashion when Sione Katoa skirted down the touch line, while fellow winger Ronaldo Mulitalo finished with a double.

Tom Hazleton laid on another try for the Sharks when he passed before the line for Jack Williams, but finished the game off the field with a knee complaint.

Sharks back-rower Briton Nikora also bagged a second-half double, with his second coming in easy fashion when he ran on to a Trindall ball and burst through.

Cronulla's only other real concerns were Jesse Ramien being placed on report for a high shot, and Williams for an early hip-drop tackle.

AAP