Chants of "Papa" rang through GIO Stadium after the Raiders legend's two late tries, before Papalii converted his second himself to put the icing on a 36-12 victory and send the Raiders to the top of the NRL ladder on Sunday.
Despite the veteran's late show, it was young five-eighth Ethan Strange who was responsible for turning the day around for the home side, after two early Rabbitohs tries for Keaon Koloamatangi and Alex Johnston threatened to rain on Big Papa's parade.
Strange was unstoppable in wet and near-freezing conditions that made handling a tricky task.
Just before halftime, the 20-year-old showed why he is one of the best running halves in the league by pushing past four Souths defenders to muscle his way to the tryline and lift the Raiders back into the game.
Until then, Canberra had looked bereft of ideas in attack, but momentum suddenly swung their way.
Strange replicated his effort after the break, jinking past more flat-footed defenders to put the Raiders back level.
Soon after, Johnston failed to defuse a Jamal Fogarty bomb and back-rower Zac Hosking cleaned up the scraps to send Canberra ahead.
The Raiders grew in confidence and doubled their lead through Simi Sasagi before Papalii, who was given a rare start by coach Ricky Stuart in his 319th game, came on for his second stint.
In the 70th minute, the strong crowd of 19,438 that braved the miserable conditions were sent into raptures when hooker Owen Pattie sent Papalii over with a short range pass.
Three minutes later the veteran went over after another Pattie pass and stepped up to land the conversion.
The Raiders went top with the result, though Canterbury could usurp them when they face Parramatta on Monday.
Other than a brief moment in round 2 of 2024, it's the first time Canberra have topped the ladder since round 6 in 2005.
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