The front row set the platform and centre Trinity Spooner-Neera was on song with a slight wind advantage to land four straight penalties and extend the visitors to 12-3 approaching halftime.
Coach Jason Caskey was waiting for that big blow to put the game away, especially after the team held firm, giving away just three points, following a sin binning just after the break for the second-straight week.
Referee Cameron Stone judged lock Jon Smyth had made a no-hands shoulder charge.
The nerves were jangled for all observers in a pulsating opening 10 minutes of the fourth quarter. First, winger Michael Nabuliwaqe pounced on a turnover at halfway, hacking the ball ahead and then keeping it on the toe before fellow speedster Samu Kubunavanua won the foot race, for 19-6.
Mid Canterbury hit back four minutes later as inspirational captain Jon Dampney, always up for a big game against Wanganui, crossed over 4m from the touchline.
But in a big moment, fullback Andrew Letham's conversion struck the near upright to leave the home side still outside striking distance at 19-11.
Second five Poasa Waqanibau snatched an intercept and was burning off the opposition other than one Mid Canterbury winger, but right at the point of diving under the posts the ball came free - a fumble that could not happen again to the standout Fijian in 100 replays.
Not long after, Spooner-Neera had a straightforward 30m penalty attempt right in front but somehow his otherwise radar-like boot deserted him, leaving Caskey with that sinking feeling of deja vu.
"Put it this way, we were the better team. There was a couple of stutters," he said.
But this time his men would not be denied. If luck was not with them then they would make their own.
Reserve No8 Ranato Tikoilosomone had come on to play strongly after linchpin Bryn Hudson aggravated his prior calf injury with 20 minutes left, while everyone in the engine room from lock Sam Madams to flankers Fraser Hammond and Peter Rowe were putting in a yeoman's effort.
Desperate, Mid Canterbury threw the long loopy pass and livewire schoolboy Stephen Perofeta swooped to pluck another intercept, then two passes later Dibben was on the outside of his man and going under the posts with time up on the clock.
"The forward pack got stuck in. Most of the team played well - they kept composure," said a relieved Caskey.
Proud captain Rowe said props Viki Tofa and Kamipeli Latu were excellent.
"They had a bit of a point to prove from last time. They were the fellas that set the tone. They were easy to follow.
"We left at least a certain 10 points out there. A bit better than what the score showed.
"[Mid Canterbury] were trying to score - the boys were coming forward and making the tackles. The boys really defended well, so there was always that confidence we could do it. They stuck at it."
Caskey said Hudson should still be all right to front for this coming weekend's Meads Cup final and Rowe said his calf problems will not be a factor: "I'll be good to go. I can't not be."
The final was so nearly a home Cooks Gardens match because in the other semifinal a brave Wairarapa-Bush were ahead of 2015's juggernauts South Canterbury before being pulled down 25-21 in Timaru.
However, both Caskey and Rowe have confidence they can make yet another successful South Island sojourn, as Wanganui's road game record stands at a perfect 5-0 this year.
"The boys enjoy travelling and getting away together," said Rowe.
"We've performed well away from home. It's finals footy. Anything can happen."
Wanganui 26 (Samu Kubunavanua, Simon Dibben tries; Trinity Spooner-Neera 4 pen, 2 con) bt Mid Canterbury 11 (Jon Dampney try; Andrew Letham 2 pen). HT: 12-3.
