The minor premiership now appears a formality for the Panthers, who are the most successful team after 16 rounds this century, and could be four wins clear at the top of the ladder by the end of the round.

All but one member of the Panthers' best 13 played representative football last weekend while the NRL went on hiatus but coach Ivan Cleary opted to name an unchanged starting side for his clash at BlueBet Stadium.

It proved the right call - but only just.

With seven of their own players backing up, the Roosters gave the defending champions their most significant challenge since their round nine loss to Parramatta.

The versatile Joey Manu started in the halves in the absence of Luke Keary (concussion) and had a hand in both the Roosters' first try and that which gave his side the lead early in the second half.

In wet conditions, the Panthers appeared reluctant to play as expansively in attack as usual but consequently found it harder to breach their opponents' defence.

Perhaps due to the weather, the Panthers' own defensive line was uncharacteristically brittle as compared to their opponents'; the Roosters' first two second-half tries came from close range and sent the Penrith crowd quiet.

But when they were struggling for momentum, the Panthers' Origin stars stood up; first Nathan Cleary sent a perfect pass to Izack Tago that helped the Panthers re-gain the lead, and then Api Koroisau burrowed over from dummy half to seal the result.

"It was a good, tough game," Panthers coach Ivan Cleary said.

"I thought the Roosters were really good tonight, which we expected.

"I was really happy that we managed to get in front and then score again."

The Roosters had only 28 per cent of the territory and were wrong end of an 8-3 penalty count, leaving coach Trent Robinson to call the refereeing into question.

"There were so many poor decisions tonight," he said.

He singled out the referee's decision to penalise Sam Verrills for a supposed dangerous tackle, which put the Panthers in position to score, and the sin-binning of Angus Crichton after the play had moved past his professional foul.

"They're big decisions that you can't get wrong," he said.

"It wasn't good enough."

NSW coach Brad Fittler would have been watching nervously when Panthers and Blues centre Stephen Crichton appeared to tweak his hamstring in the first half.

But Crichton managed to remain on the field and the Panthers confirmed the injury was not a concern to medical staff at halftime.

"It was just a bit of a nerve problem. He's all right," Cleary said.

Playing his first game since mid-May, influential lock forward Victor Radley left the field early for a head injury assessment.

The Roosters will hope not to lose him for any more games; they won only one of five when he was sidelined with an ankle injury.

Australian Associated Press