For all the football Rangiuru played in the opening stanza, it was their opposition that provided its biggest highlight.
Caleb Foster's 60m effort and the resulting conversion from a slick Robbie Tai closed the gap to 14-7.
Rangiuru went into the break 14-10 up, but kicked out at the beginning of the second half. Their large backline delivered another try down the flanks to make it 21-10, before Nicolas put a nice in-and-away on down the right-hand side to seal the deal.
Edward Maui barged his way over from close range in the final 10 minutes, but by then the match belonged to Rangiuru.
The win gives them sole possession of the competition lead, with memories of last year's narrow brush with the premier division no doubt still fresh in their minds.
Coach Peter Woods said simple rugby was the key to getting the result.
"It's good rugby and the boys are finally clicking on to it - it's pleasing for a coach," said Woods.
"We thought whoever made the least mistakes would win and that sort of went our way in the end.
"The first half was what we worked on all week - keeping the ball in hand and putting or phases together. We bombed probably two [tries] in the first half with our guys dropping the ball, but that will happen."
Rangiuru 28 (Elijah Nicolas 2, Patuara Biel, Ra Faulkner tries; Sasu Wihapi 4 cons) beat Poroporo 15 (Caleb Foster, Edward Maui tries; Robbie Tai pen, con).