Down two points and looking to complete a spirited second-half comeback, Canterbury winger Brett Morris grubbered ahead only 10m out from the Roosters line and the Bulldogs regathered the football.

Hasler thought the referee waved his arm to indicate six-again, but the call was then seemingly overturned and the Roosters ended up with the ball.

"I thought the head referee called six-again, then it gets overruled by the pocket referee or the touchie [touch judge]," Hasler said.

"I know he might have panicked a little bit because when he was asked about it by our captain ... his words were 'no I didn't call six-again, my hand was up for the last'.

"To me his action looked like six-again.

"You think the referee as the head referee has a clear call on it. He played at the ball so I don't know how a touchie or the pocket referee would overcall a head referee.

"It wasn't the reason why we didn't win the match but it's crucial. It was good field position for us and I thought we had good momentum."

The Roosters raced to a 20-6 half-time lead before Canterbury staged what is fast-becoming their customary second-half fightback.

But Roosters halfback Mitchell Pearce ended any hopes of a Bulldogs win with a late try to seal the victory, and most likely his number seven jersey for NSW.

"They managed it better than what we did at the end of the day, they're a very good football side, you have to keep possession away from them," Hasler said.

"You need to get even possession. They were running at about 64 per cent in that first half, they capitalised on it. We came up with some uncustomary reads in D [defence] which gave them field position.

"At 20 to six down against a team like that I was pretty pleased at the way we came back in the second half. We showed good courage to get back in."