Sydney Roosters prop Sam Moa had to convince coach Trent Robinson at halftime that returning from a dislocated kneecap in the pressure-cooker final against Manly would inspire, not backfire.

However, that tough sell to the boss was nothing compared to the battle he first had to win in his own mind.

The 27-year-old spent 20 minutes deliberating whether he would be letting his team down by attempting a comeback.

Moa felt his kneecap pop in and out just three minutes into the contest and hobbled off the field, seemingly long odds to return.

His contribution helped the Roosters repel Manly 4-0 in an epic encounter at Allianz Stadium on Saturday night that earned the tri-colours the all-important week-off.

Moa admits he had his doubts.

“I was just thinking in my mind whether it’s worth to go back on and I was worried I would let the team down by missing a tackle or not performing,” Moa told AAP.

“It took me about 20 minutes to decide and the way the game was going I didn’t want to miss out on all the action.

“I just backed myself and said go hard or go home.”

Moa denied his efforts were heroic, but coach Robinson hailed the NRL late-bloomer’s 15-minute second half spell has game-defining.

“I didn’t think he’d be able to go back out there and at halftime he said, ‘I’m right to go,'” said Robinson.

“I said, ‘are you ready to play or ready to perform?’ And he said, ‘I’m ready to perform’, and that’s what he did.

“The way he carried the ball, got us back going through the ruck and there were some really important carries from him.”

Moa admits he’s exceeded his own expectations this season, in contention for a World Cup berth with New Zealand after a breakout first full year in the NRL.

He played one match for Cronulla back in 2008, before plying his trade for four years with Hull in the English Super League.

The Tongan-born bookend said finding himself one game away from a grand final was hard to believe after arriving at the Roosters with a humble goal of fighting for a place in first grade.

“I was more worried about coming back and getting used to the training and fitting into the team. With such quality players right across the board I was just focused on training hard and getting my spot anywhere in the 17,” he said.

“I’m just so grateful I’ve come back to such a good team and it’s not hard to play good footy when you’re playing with the calibre of player we’ve got here.

“I think I did my apprenticeship overseas and the time was right to come home.”