Defending NRL champions Sydney Roosters got off the mark this season with a 26-18 win over Manly Sea Eagles.

The Roosters were undone by rivals and early pacesetters South Sydney Rabbitohs in their opener but returned to form on their travels on Saturday, with scrum-half Luke Keary instrumental in attack.

Lachlan Lam made his NRL debut for the Roosters with Cooper Cronk missing due to a hamstring injury, but the veteran half-back's absence was not felt.

Having scored a hat-trick in the Roosters' World Club Challenge win over Wigan Warriors, Brett Morris opened his NRL account for the club to break the deadlock.

Daniel Tupou, also on the scoresheet against Wigan, made it three tries in two NRL games with a first-half brace sandwiching a Boyd Cordner effort. Tupou's second saw the Roosters finish the half in style as he collected a superb Keary chip to send Sydney into the break 22-0 up.

Cordner increased the gap with his second after the interval, pouncing on a Lam grubber kick. Manly fought back through Manase Fainu, Jake Trbojevic and Moses Suli but the deficit proved too great for them to overcome as they remain winless.

Penrith Panthers also claimed their first victory of the season, holding off a late rally from Newcastle Knights to claim a 16-14 away win. 

James Fisher-Harris and Frank Winterstein crossed to give Penrith a 10-8 lead at half-time, with Isaah Yeo stretching their advantage after the break.

Mitchell Barnett frayed Panthers nerves by trimming the gap eight minutes from time but Penrith's defence held firm for the points.

Cronulla Sharks scored all their points in the first half of their maiden win of the campaign, Sione Katoa's double helping them to a 20-6 defeat of Gold Coast Titans.

Nilled by Canberra Raiders last time out, the Titans did at least get their first points of the season via Brenko Lee's try, but have plenty of work to do with a miserable start leaving them bottom of the table.