With Cooper Cronk (hamstring) and Jake Friend (shoulder) missing, the reigning premiers shuffled the decks with Keary shifting to halfback and Latrell Mitchell to five-eighth, only for those plans to fall through when Brett Morris was helped off at halftime with a suspected knee injury.

The changes mattered little as the new-look halves pairing tore the hosts to shreds in a first-half blitz at Lottoland that saw the visitors open up an unassailable 22-0 lead at the break.

Roosters coach Trent Robinson credited Keary, who set up all four first-half tries, for being able to step up as the chief shot caller, while also reverting to his eyes-up play when the opportunity arose.

"Luke's been an incredible five-eighth for us in the way that he makes those instinctive plays and then Cooper's out and he has to make the switch where there's more of a game-management sense in him," Robinson said.

"I thought in the first half he really controlled the game and then he had the ability to play his plays.

"The balance between the two was high class."

Keary, last year's Clive Churchill Medallist, was on from the outset on Saturday night as he set up Morris and Daniel Tupou for tries before he poked his nose through the line and popped an offload in traffic to send Boyd Cordner over to make it 16-0.

Fullback James Tedesco roared back into form as he shot through late in the half before Keary found Tupou with a pin-point kick to cap a faultless 40 minutes.

The fill-in halfback was forced off early in the second half but was able to return as his side increased the lead when when Cordner shrugged off a high shot to score off debutant Lachlan Lam's grubber.

The Manly crowd of 9664 was rewarded for braving monsoonal conditions in the first half when Manase Fainu crashed over in the 58th minute, and there was a glimmer of a comeback when workhorse Jake Trbojevic backed up a break to score in the following set.

The clock proved the hosts' biggest enemy, although Moses Suli pounced onto a charged-down kick to score the game's final try.

"You can't always be relying on the adage of the second half," Sea Eagles coach Des Hasler said.

"We got 18 points and it was brave, there are plenty of good signs there, but those good signs have got to turn into points; and we've got to start winning."

Australian Associated Press