Koloamatangi and Knights centre Bradman Best will make their Origin debuts as part of a new-look Blues squad out to avoid a clean sweep in the series finale at Accor Stadium on July 12.
Other changes include the selection of Rabbitohs No.6 Cody Walker, Eels pair Clint Gutherson and Reagan Campbell-Gillard, Manly forward Jake Trbojevic and Newcastle prop Jacob Saifiti.
The Rabbitohs, who also have Cameron Murray and Damien Cook in the NSW team, could have equalled their biggest Origin representation if centre Campbell Graham had been fit as he was in contention but has a sternum injury.
Walker replaces Penrith’s Jarome Luai at five-eighth, while Murray’s selection at lock forces Isaah Yeo to the bench alongside Gutherson, Saifiti and North Queensland rake Reece Robson.
For Koloamatangi, selection in the NSW second row is the fulfilment of a childhood dream he shared with Murray as they grew up together playing for Mascot Jets, but a series of injuries jeopardised the 25-year-old’s ambitions.
“He came through Mascot and he is a genuine Souths junior, but he had a lot of injuries when he was 16 and 17-years-old,” former Rabbitohs GM of football Shane Richardson said.
“Because of the injuries he didn’t play a lot of footy, but Willie Peters fostered him and kept him in the squad.
"He came back late in the season in Willie’s SG Ball side that made the  grand final and he was just about the best player, even though he hadn’t played all year.
“Willie Peters kept saying this kid is special – and really special – and myself and Mark Ellison jumped on board because we could see his potential too.
"He was one of those guys - like Cameron Murray and Campbell Graham – that you earmarked for big things.
“He could have dropped out because of the injuries that he had but he didn’t. He stuck with it and came through the ranks pretty much unheralded because he hadn’t played a lot of rep footy.”
Koloamatangi credits his father Izzy and mother Nicole as his biggest supporters, so he was disappointed they had missed his NRL debut against the Storm at AAMI Park in 2020 because of COVID travel restrictions to Victoria.
The June 4 match was in the first round after the Telstra Premiership resumed following a 10-week COVID-enforced shutdown and teams flew to and from interstate games on chartered jets to play in closed stadiums.
“It wasn’t like a proper debut, it sort of felt like an under 20s game,” Kaloamatangi told Rabbitohs.com.au.
“Because of COVID we had to get our own plane. We got there four or five hours before the game and we had to stay at the field, we couldn’t go to a hotel or anything like that.
“It was unfortunate that my parents couldn’t be there to see me make my dream debut. They have been to every single game they could go to, but I didn’t want to just play one game, I wanted to play as many as I could for the club.
“They stuck by me through a lot, and I am very thankful to them, so the least I could do was play my best footy and train as hard as I can.”
Even before his NRL debut, Koloamatangi had been in the sights of Tonga coach Kristian Woolf, who believed he and the likes of David Fifita could help the Pacific nation win last year’s World Cup after beating Australia, Great Britain and New Zealand before COVID stalled the international game.