It was not long before Rangiuru hit back, with abrasive flanker Terry Wilson crashing over from close range after a succession of phases to make it 5-5.
A touch of class from pivot Sasu Wihapi, who dummied and stutter-stepped before putting a perfect kick to the corner that Jordan Kendall dived on. The kick was unsuccessful, and when Rob Tai kicked a penalty to narrow the gap to 10-8, the match had developed into a classic arm wrestle.
Maxwell crossed for his second before the half and Tai added five points with the boot, and all of a sudden Poroporo were eight points up after 32 minutes.
Rangiuru raged back just before the break and likely had a legitimate claim to a penalty try and a yellow card after a flowing attack down the right-hand side was interrupted by a deliberate knock down.
The resulting penalty for an earlier indiscretion narrowed the gap to 18-13 at halftime - not much considering the swirling breeze was to favour Rangiuru coming home.
Rangiuru's goal kicker was one of a number of kickers to struggle in the conditions, but nailed a 52m penalty to make it a two-point game after 56 minutes.
A pair of missed penalties followed before Rangiuru hit the front 19-18 through another penalty. Rangiuru cleverly used the wind and put their opponents under pressure, forcing Poroporo to attack from their own end.
Sasu Wihapi then clinched the final, swooping on an errant pass to race 30m to score next to the uprights.
The conversion made it 26-18 with five minutes to play, leaving Poroporo no alternative but to run the ball into the teeth of the surging Rangiuru defence.
The final whistle sparked scenes of wild celebration, and surely many moves in the offseason to strengthen a side destined for the premier division - and a pair of massive derby matches against Te Puke Sports - next season.
Rangiuru coach Peter Woods was a relieved man after the trophy presentation.
"It's been a struggle," he said. "The team hasn't been up for a few years now and especially with the result of last year, it's definitely pleasing to finish it off this time around," said Woods.
"We floundered about a bit down there and I told our first five Sas to get it down there and win the game for us. He put in some good kicks and we put them under pressure."
Woods was under no illusions about what awaits in the top division next season, with the unofficial campaign to stay in the top flight likely to have already started.
"There's a lot of planning to do, a lot of work. We saw with Paroa this year how hard it is and it's not going to be any easier for us. We are recruiting - there's a lot of talented young guys who go elsewhere to play - but with us being in the premier division they might come back."
For Poroporo, the loss was bitter sweet. It was their first appearance in a Division One final, and it came at the end of historic year for the club in several respects. They have plenty of promising young talent coming through - no more so than Rob Tai - and loom as a threat next year to be the next side from Division One to win promotion.
Rangiuru 26 (Terry Wilson, Sasu Wihipi, Jordan Kendall tries; Ngati Kingi 3 pens, con) Poroporo 18 (Robert Maxwell 2 tries; Rob Tai 2 pens, con).