Prop Shaun McDonough ran with venom and left his mark on Pirates defence, as did lock Nick Cranston who carried three tacklers under the posts to score what proved the back-breaking try after 52 minutes.
Likewise, Ruapehu's kicking game has not often been highlighted and throughout the opening 40 minutes first-five George Williams, fullback Zyon Hekenui and even flanker Andrew Evans were pinpoint.
Williams being sinbinned for a professional foul did not halt their stride as Evans regathered a charge down by centre Tautahi Rawiri to get the Ruapehu's opening try.
Rawiri was also on with his goal kicking in difficult conditions.
For Pirates, inspirational captain Lasa Ulukuta tried everything to exert pressure, while centre Samu Etuaiti showed little signs of rust from his enforced layoff to be a danger out wide at every turn.
But when Ruapehu turned aside around 15 minutes of continuous pressure through the middle stages of the second half, it was clear the visitors had no answers.
Winger Robert Hughes crashing over in the corner with time up may have left a scoreline which doesn't quite reflect the games' close nature, but it is a fair nod to Ruapehu's ascendancy.
While he always talks one game at a time, Ruapehu coach Chris Winter acknowledged he was pleased the Pirates curse was lifted.
"Most definitely, no doubt it will give the boy's confidence.
"Defence will win these games, something we worked on. We just keep on rolling."
Pirates coach Phillip Morris knew they had been outplayed.
"We couldn't set a platform, too many turnovers.
"Forcing passes and it didn't click on the day."
"Ruapehu's defence was outstanding. Their defence wins games."
What was telling is Pirates started so confidently against the favourites setting up fullback Josh Marwick to have a number of opportunities to boot them to a 6-3 lead after 24 minutes.
But Ruapehu calmly kept boot to ball and when Rawiri punched a chip through he again crowded the busy Marwick and charged him down, with Evans right there to score the crucial five pointer.
Pirates threatened on many occasions to break out in the second stanza as Etuaiti, Ulukuta and winger Clive Stowers created their share of line breaks.
But working down to a 5m scrum, first Hughes had a crack and then Cranston opened Pirates up right under the black dot.
Rawiri slotted his third penalty as Pirates patience began to wear thin, then Hughes wrapped it all up by toeing through a Williams grubber kick and showing great hands to regather and score.
McCarthy's Ruapehu 28 (Andrew Evans, Nick Cranston, Robert Hughes tries, Tautahi Rawiri 3 pen, 2 con) bt Integrity Motors Pirates 6 (Josh Marwick 2 pen). HT: 13-6.