Penrith No.9s have always made a point of being the difference in Panthers’ grand final wins.

Think Royce Simmons in 1991, who scored two tries in his departing game against Canberra and was unlucky not to win the Clive Churchill Medal.

Or Luke Priddis in 2003, the Penrith hooker who scored one try and set up their other two to rightly earn him the top individual prize.

And in 2020, Api Koroisau will be just as important at dummy-half.

Just like in 2003, Sunday is expected to be wet.

It’s likely to leave it as a battle in the middle, where options and good service are also everything out of dummy-half.

“He’ll have a very big role. He’s the man that touches the ball more than anyone else every game,” coach Ivan Cleary said.

“His defence is something that’s probably been underrated. He defends a bit differently to the other guys in our team, which helps.

“He’s up the top of the tackle count each week, and he’s had a great influence on our attack as well.”

Koroisau is just the man Penrith need for the job

The 27-year-old was Penrith’s best in last week’s win over South Sydney, and has helped change the way the Panthers attack in 2020.

He’s arguably been the buy of the year, with Penrith’s fate potentially swinging on a last-minute decision to head to the Panthers over Canterbury.

“That (whether he is buy of the year) is not for me to measure that but I’m pretty happy with him, yeah,” Cleary said.

“He’s a real leader in our team, he’s been there and done it before so that helps.

“Yet he’s still the cheeky nine-year-old each and every day.”

The job Penrith do on Koroisau’s opposite number will be just as match-defining.

Last week they contained Damien Cook perfectly, denying the Rabbitohs quick play-the-balls and keeping him to just one run.

But Cameron Smith is a different kettle of fish.

While Cook and Koroisau are dangerous when they run, Smith is the conductor who manages the game better than anyone and picks out his men.

At age 37, the Storm captain leads all hookers for try-assists this year, with the 17 teammates he has put over the equal-most in his 19-year career.

“The main thing with Cameron is if we give the Storm enough opportunities and time in good field position, he’s good enough to know what to do from there,” Cleary said.

“That’s the biggest fear for me is that with the great players you don’t know what they’re going to do necessarily but that’s their whole team.

“There’s the big moment that the great players come up with the best plays.”