The game was quite chippy, with multiple penalties for dangerous tackles going against both sides.
Otangarei went on a game-changing fourteen-minute blitz, scoring 22 points.
It started when fullback Jordan Katene made a 70m bust from dummy half to cross for his first try.
Winger Dominic Ormsby then broke the line off the kickoff, nearly going the length onf the field, but Portland scrambled to stop him.
They couldn't hold out though as standout hooker Samuel Henry snuck over.
Henry crossed for his second four minutes later, against diving over from dummy half.
Otangarei capped off their first half with a try in the corner from Pedro Blake after good ball movement.
Lock Verne Wilson added the extras on four of the first half tries to give them a 28-4 lead at the break.
The tension between both sides hit tipping point ten minutes into the second half when Portland's Tukurangi Metua was sin binned for a lifting tackle.
Rather than succumb to losing a player for ten minutes, Portland immediately brought themselves back into the contest with a try of their own.
Once Metua came back from his enforced break, Otangarei resumed order with a try to Ormsby.
Katene then crossed for his second and third tries, giving them a 40-10 lead.
Portland crossed for two consolation tries to add some respectability to a scoreboard that belied their efforts at Toll Stadium.
Otangarei had the final laugh however, with Katene putting the icing on a truly impressive outing with his fourth try.
Otangarei will return to Toll Stadium next week looking to make the grand final when they take on Moerewa.
Moerewa went down 36-28 to Takahiwai in the grand final qualifier, earning Takahiwai a week off.
