The match then turned into a kicking duel and that left Ruapehu fullback Mitchell Millar, who still gave a gutsy effort, being outnumbered against Taihape's leading lights in halfback Ra Broughton, fullback Tyler Rogers-Holden, and the indomitable Whale brothers – first-five Luke and centre Dane.
Those aforementioned kickers weren't flawless in their approaches – both teams of missing touch or kicking out on the full when they shouldn't – but Taihape are familiar with penalty-dominated affairs and Dane Whale once again proved the man for the big occasion by landing six kicks from eight attempts.
That gave enough of a lift for Taihape's slightly smaller but inspired forward pack to dig a little deeper, as prop Wiremu Cottrell, hooker Dylan Gallien, lock Peter-Travis Hay Horton and flanker Matt Brown gave sterling service for breakdown after breakdown.
Hay-Horton and Brown also managed to steal several crucial lineout throws off Hart, given Ruapehu hooker Roman Tutauha was having another fine match until early in the second-half when he took a hard knock and was slowed noticeably for the rest of the game.
Down by three points, and then six with less than ten minutes left, Ruapehu were still the team most would back to find their way home, as they have so many times in the past.
Taihape had all but struck the killer blow, as they got held up under the posts and then lost the ball with the line begging – eventually settling for Whale's fifth penalty and steeling themselves for an avalanche of home town pressure with the clock ticking away.
Ruapehu responded in classic style – working through penalty lineouts and then driving right to the tryline chalk, but the defenders held them off twice, helped by the fact Ruapehu had to work back from midfield after a couple of their passes and kick retrievals slipped from hand.
One more Taihape lineout steal, only 5m from their tryline, and appropriately it was Broughton kicking the ball dead to set off wild scenes of jubilation from the underdogs, who have qualified for their first grand final since 2016.
"Definitely you have a chance," said delighted coach Tom Wells, who a fortnight ago before following their loss to Wanganui Car Centre Kaierau had privately mused his team would prefer an Ohakune playoff to Waverley.
"The first 20 minutes they were putting the ball in behind us and we were under [pressure].
"Then we cottoned onto that. Ra [Broughton] was awesome with the box kicks.
"Whoever made the least errors on the carry was going to win it.
"Two unreal packs going hard – two front rows going at each other. Just so tight."
The coach was loathed to inflate Dane Whale's head too much after a clutch performance, similar to his prior exploits in the Steelform Wanganui jersey, but the play-maker had given a full account in a water-tight fixture.
"It's just a matter of him getting his heart and head aligned.
"But he's got a lot of experience around him."
After an 11-1 season had come unstuck one week early, Ruapehu co-coach Kim McNaught agreed they would regret the little 50-50 moments where Taihape delivered and they didn't.
"They just probably wanted it more than we did. The weather was a leveller.
"They played the territory game well.
"Good luck to them – hopefully a Northern [sub union] team can lift it next week."
Early on, it seemed Ruapehu had the best handle on the rain and mud, as following a Taihape clearance to midfield, Ruapehu spread the ball and centre Tautahi Rawiri put down a well-weighted grubber kick for second-five Troy Brown, who showed great composure to slide down onto the ball and trust mud and momentum to take him over the tryline, without reaching out for a double movement.
But that would be it for midfield set plays, with neither team able to work hard-running players into gaps, due to the weather.
Millar getting isolated on a couple of Taihape kick-and-chase plays let the visitors work back upfield, and then referee Aaron Conlon pinged the home side for hands at the ruck, allowing Whale to close the gap to 5-3.
Taihape kept looking to reach the far sideline corner on their midfield touch-finders, and from a lineout in good position, Broughton fed a charging Gallien down the blindside through a half gap, and the hooker set up big winger Jaye Flaws to charge in at the corner flag, with Whale dropping his great sideline conversion just over the cross bar.
Down by five, Ruapehu didn't panic and just two minutes later, with Taihape offside from a bomb, they went to the sideline and the pack drove off Hart to set up Tutauha diving over for a signature forwards try from the two-time defending champs.
Millar was away with another sideline attempt, and with the sun coming out, Taihape again worked forward through getting the better of the tactical kicking duel and then earning successive penalties on their hit ups.
Whale landed his third straight kick for 13-10, which stayed the score till halftime, after the centre had his first miss with six minutes left.
As the rain returned following the break, so did Ruapehu's execution, as despite Tutauha's injury they worked forward through one-off carries to get a penalty in front on the 22m line, and Millar was settled to lock the scores up in the 48th minute.
Then followed immediate tit-for-tat scores, as a daring chip kick and grubber kick raid by Rogers-Holden and winger James Barrett, another standout, saw Ruapehu infringe while fumbling the ball in front of their tryline.
Whale added the three points, but Taihape had to scramble out a bouncing kickoff ball and Hughes earned his team another penalty from the attacking ruck, with Millar slotting it from 33m out.
A bone-rattling hit by Hay-Horton on flanker Jackson Campbell saw Ruapehu lose the ball midfield, and Ruapehu were penalised for coming up on Rogers-Holden, with Whale putting his penalty kick just offline.
Trying to out-think the home side, Taihape risked a couple of quick taps on penalties, while a couple of Ruapehu's lineout throws not going straight left them trapped in their corner.
The home defence held, with prop brothers Te Uhi and Gabriel Hakaraia being a stonewall, yet the home side making two big fumbles right in front of their posts from the scrum win saw Taihape No 8 Tremaine Gilbert all-but score.
After the Taihape scrum, Cottrell had a go at the tryline but just couldn't hang onto the ball, yet Taihape stayed cool as they worked back from Ruapehu's clearance and got the penalty, with Whale landing it on the angle for 19-16 with 12 minutes left.
Rogers-Holden kept putting the ball into the corners and the Ruapehu wingers were under pressure, with Will Scarrow being injured after claiming a chip kick, and a frustrated home side back-chatting to Conlon only earned Taihape another penalty, which again Whale delivered on the other angle.
With five minutes left and needing a converted try, Ruapehu drove 11.5m from a 12m penalty lineout to all but score, with Taihape locking the ball up to get the turnover before the attackers could reset, and then one final lineout steal off the last play let the underdogs kick it out to complete their stunning upset.
Taihape 22 (J Flaws try; D Whale 5 pen, con) bt Ruapehu 16 (T Brown, R Tutauha tries; M Millar 2 pen). HT: 13-10.