The 19-year-old centre, one of two late-season debutants for the Knights alongside Oryn Keeley, made back-to-back NRL appearances in rounds 23 and 24.

He came into the side after Bradman Best was dropped for disciplinary reasons and held his own on debut against Canberra, earning another start against the Gold Coast where he produced a similar showing.

Knights coach Adam O'Brien had planned to play Mapapalangi in the club's last game against Cronulla, but gave him the option to return to Jersey Flegg for the side's finals campaign.

"Maps", as he is known at the club, chose to return to the under-21s team he began the year with.

"I thought it would be best if I play Flegg, just based on the fact that I started there and it would be good for not only the club, but Newcastle, if we can win the grand final," he said.

Newcastle face Penrith in the CommBank Stadium decider at 1pm on Sunday.

The Knights finished the regular season second but have enjoyed a week off after beating Penrith (22-16) in the first week of the finals followed by minor premiers Sydney Roosters (24-22).

Mapapalangi has the added motivation for the game of having never played in a representative grand final.

Signed by the Knights midway through last year, the Maroubra Lions junior played Harold Matthews (U/16s) for South Sydney and S.G. Ball (U/19s) at both Souths and then Manly.

The centre/five-eighth trained with Newcastle's NRL squad last summer but was overcoming shoulder surgery.

He had a few games of Jersey Flegg to start this season but mostly played NSW Cup before being called up to the first-grade side.

Reflecting on his debut in Newcastle's 28-22 loss to Canberra, Mapapalangi said he had an inkling he might get a start in first grade late in the year but found the experience no less daunting.

"During the week, I couldn't sleep - I was nervous," the Concord product said.

"The first two nights were probably the worst sleep I've had this year.

"But then it got a bit easier as it got closer to the game.

"The boys were reassuring me they had my back on the field and just to have fun and enjoy it."

Mapapalangi had a support crew of about 100 family and friends attend his debut.

A Facebook post by his Tongan father prompted the turnout with some family flying in from Queensland.

"When I seen them in the corner warning up, it just gave me that extra confidence," Mapapalangi said.

"Without their support, I wouldn't be where I am today."

Mapapalangi said he had gained confidence from his two NRL appearances and from the help of the likes of Dane Gagai, Hymel Hunt and Edrick Lee at training throughout the year.

Jersey Flegg coach Tony Gleeson said Mapapalangi's defence had been his greatest improvement in 2022.

"He's realised if he can match it in first grade in defence, than he is more than capable of doing that in the 21s," Gleeson said.

"He has brought that air of confidence to the team as well.

"He's been a real positive for us."

Having had a taste of the NRL, Mapapalangi is unsurprisingly keen for more.

Upgraded from a development contract to the club's top-30 roster, he is eyeing, and hopeful, an uninterrupted summer will help him push for a place in the NRL side next year.

"I'm going to have a big preseason and try and secure my spot in the centres," he said.

"Try and play round one."