"A lot of teams would have dropped their head after that [first half] intercept try," said coach Duane Brown.
"But we've got a whole lot of youth and experienced players.
"We knew we had to go wide on them, or be physical up front at the same time."
Dotting down to snatch the game were flanker turned lock Ivan Syme and 20-year-old winger Kotahi Paranihi, nephew of Aaron, who got the match-winner in the corner to claim player-of-the-day.
Marist have some pace as fellow talented winger Rangi Kui, 18, transitions from Celtic to also having an impact with the Dave Hoskin Carriers Marist Premier team.
Guys like prop 'Tank' Hina and back Michael Flood have contributed, while the side is very much buoyed by the return of playmaker Steelie Koro, the former Steelform Wanganui captain with 51 Heartland games, who spent the past two years coaching Harvey Round Motors Ratana.
Celtic have predominantly the same squad as their 2018-19 campaigns, where they managed a win in each season against Senior's powerhouse club Kelso Hunterville, including last year to knock them out of contention for the inaugural Division 2 competition.
But Brown admits it is the pain of the 2018 loss in the Senior final – 23-10 to Hunterville – that is driving his veterans.
"We got a few guys straight out of high school, which helps our 40-year-olds who probably should have stopped a season ago. But one more time."
This unique 2020 campaign, where 11 teams play one round so just two of them can qualify for a straight final, means Brown knows they cannot afford any slip-up with five games left.
Beating Kaierau was one season goal, while the others are Hunterville and Ratana, the latter being a contender for the final alongside Utiku Old Boys, as they both still have a game in hand on Celtic.
"Our goal is to score bonus point wins right through," said Brown.
Next on that agenda is Speirs Food Marton at the Racecourse grounds this Saturday.
The draw is
Senior (1pm kickoffs): Celtic vs Marton, Racecourse 1; Pirates vs Taihape, Cooks Gardens; Buffalos vs Hunterville, Spriggens Park; Utiku OB vs Kaierau, Taihape.
(2pm kickoff): Ratana vs Counties, Ratana Pa; Border bye.