Joseph Manu has produced a stellar performance at five-eighth as the Sydney Roosters registered a crucial 54-26 NRL win over St George Illawarra.

An astonishing individual performance from Joseph Manu has inspired the Sydney Roosters to a fast-finishing 54-26 win over St George Illawarra that snapped a four-game NRL losing streak while keeping their finals hopes alive.

But the victory in Gosford looks to have come at a significant cost for the Roosters, regular first-graders Billy Smith (ACL), Sitili Tupouniua (ACL) and Siosiua Taukeiaho (cheekbone) going down with injuries.

Moses Suli limped off for the Dragons just before halftime and was seen in a moon boot on crutches post-match.

Both sides have designs on playing September football despite going into the round sitting outside the top eight.

With Luke Keary still missing through concussion, Manu shifted to five-eighth for just the fourth time in his career and wasted little time exerting his influence on the contest.

He first barged through the middle of the park and flicked the ball away to Victor Radley, who opened the Roosters' account against the run of play.

Five minutes later, Manu forced a drop-out with a kick to the in-goal area, and made the most of the ensuing field position by barging over from dummy-half.

In the first half, Manu's efforts were matched by Dragons captain Ben Hunt.

Hunt brought his State of Origin heroics to the Central Coast, spinning out of the Roosters' goal-line defence for the Dragons' first try and then landing an inch-perfect 40/20 kick to lay the groundwork for their second.

The Roosters' hopes of working back into the game were dealt a blow when Smith did his knee, forcing Manu to shift between the halves and the outside backline.

The tight contest threatened to swing in the Tricolours' favour when Dragons prop Aaron Woods was sin-binned for taking Sam Walker off the ball as he kicked from close range early in the second half.

Dragons coach Anthony Griffin questioned whether Woods' actions even warranted a penalty.

"It's a big play to put someone in the bin. I didn't even think it was a penalty, you're allowed to jostle on a kick," he said.

"But that's not the reason we lost ... we just weren't strong enough defensively."

The Dragons scored first while they were a man down but Manu's second try from dummy-half was the impetus for a five-minute surge that produced two more tries for the Roosters and ultimately sealed the win.

The floodgates opened with the Dragons defence capitulating once the Roosters found their rhythm.

Playing back at five-eighth, Manu set up the Roosters' eighth try up with a kick for Paul Momirovski and earned a well-deserved early mark.

"I'm really lucky to coach guys like 'Teddy' (fullback James Tedesco) and Joey," said Roosters coach Trent Robinson.

"You don't have to coach them much at all. They know the game better than you. You have to create an environment so they can perform, that'll all our job is."

The Roosters were down on numbers but mid-season recruit Matthew Lodge only made it onto the field for his club debut at the 50-minute mark.

He finished with 92 metres but threw an intercept pass that gave the Dragons a chance at storming back into the contest with 15 minutes to play.

The win will be crucial for the Roosters their hopes of playing finals football.

Had they lost, the Roosters would likely have needed five wins from their last seven games to finish in the top eight.

Five of those games are against sides that started the weekend in the top eight.