But fast-forward a few months and Papali'i takes "massive confidence" into a do-or-die finals clash with the Warriors, where his career began.
Over the off-season, Papali'i became a rare example of a household name recruited to the Panthers, whose premiership dynasty has mostly been built from within their junior talent pool.
At his peak, Papali'i was one of the NRL's best second-rowers, starring on Parramatta's run to the 2022 grand final.
But with the unenviable task of helping Penrith recover from the loss of James Fisher-Harris, Papali'i took time to find his feet at the new firm.
"The fitness levels was where I kind of struggled," he told AAP.
"But I understood what would get me ready for training and for the games, I knew what I had to do.
"It's just in terms of hard work, that's what wins games. That's what you've got to do week in week out.
"As much as it was hard, it was refreshing and that's what I needed personally. I've been really enjoying my first year here."
It took recovering from a minor knee injury for Papali'i to feel his season was finding its rhythm, returning in round 14 just as the Panthers began hitting their stride.
"When I came back from injury, we had a period there where we didn't have our Origin boys and we managed to string a few good games together," he said.
"That was a good confidence-builder not only for myself but the whole team.
"I guess that game fitness has kind of kicked in at the back end of the season. Keeping my job simple is what's been working for me."
Papali'i was excellent in Penrith's last game before next week's elimination final against Fisher-Harris's Warriors in Auckland.
He ran for 124 metres from the bench and crossed for the second-half try that halted St George Illawarra's momentum, with Penrith running out 40-20 winners.
Papali'i started at lock against the Warriors in round 16 as the Panthers overcame the absence of their entire State of Origin contingent to score a stunning upset win.
"We'll take massive confidence from that, and having all the boys back from that Origin side that missed out on the first game in Auckland," Papali'i said.
"(But) as much as we take confidence, it's a fresh start so I'm sure the boys will get up for next week."
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