Right on halftime Rangataua's promising halfback Akira Mako did well to score under the bar to give his team hope trailing just 13-7 at the break after having very little ball to play with.
Inspirational Ruki Tipuna finished off the best move of the match for a crucial try to give Rangataua the lead for the first time before Morris added a penalty to claw back the lead.
Then it was time for a former Maori All Black and All Blacks Sevens star to grab the game's critical late moments to win it for Rangataua.
Matua Parkinson, still fit and lean at age of 41, entered the fray with 20 minutes left to play and Tauranga Sports holding on to a tenuous 16-14 lead.
Within minutes he ran the perfect straight line to score unopposed and put his team ahead 19-16.
Then Tauranga had three attacking penalties in succession within easy kicking range but decided to take the scrum each time to try and get maximum points. Rangataua held them out in a huge momentum change in the match.
Tauranga's attempts to kick for territory deteriorated as the game wound down so they tried to run the ball out in the heavy conditions with fatal consequences. Rangataua's heroic captain Matt Clutterbuck turned the ball over and Parkinson took the final pass to dive over for the match winner.
Clutterbuck says they have been an 80 minute team this year and will look forward to the final.
"We will head to (Blake Park) with all our whanau and supporters. It is a final so you can't hold anything back, just hook into it.
"We will be there in numbers and definitely looking to do our club proud."
With the Bay of Plenty Steamers playing a Mitre 10 Cup warm-up match against Northland in Whakatane on Friday, none of those players are allowed to play finals rugby this weekend.
So Mount will lose four players and Rangataua one from their semifinal teams.
Mount will be favourites but there is no way you can right off this Rangataua side so there may well be one more twist in what has been an outstanding club season.
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