That opened the floodgates as stand-out flanker Anahera Hamahona dashed through a gap from deep in her own half, beating tacklers as she ran back to the centre and putting first-five Riana Tamati away under the posts for a brilliant try.
From a scrum near halfway, Whanganui spread to fullback Paris Munro, who dashed outside the cover and burned them off before running back behind the posts.
Whanganui were in again just before halftime as Hamahona tore through another hole to run to the posts.
Coming out of halftime, centre Keira J Mete-Renata beat her marker to run off and score.
Unfortunately for Hamoterangi, Whanganui making substitutions made it worse, as their stacked bench contained several regular starters eager to prove their fitness.
Reserve prop Waimarie Rauhina worked down the far flank and put Nepia away for her double, and then fellow reserve front rower Lavenia Nauga-Grey ran the same play for Hamahona to show a clean pair of heels - Keisha Campbell coming on to take over the goal-kicking.
Campbell then attacked down the wing and beat two tacklers before twisting through the last line of cover to get the ball down, while No. 8 Hayley Gabriel went down the other flank and just fended off her marker to sprint away for 64-0.
Nauga-Grey and Hamahona showed quick hands for Campbell to race in untouched for her double, while Mete-Renata busted through a demoralised defensive line to become the fourth player to get two tries.
Finally, reserve fullback Georgia Adams, who did not start due to feeling unwell, showed no signs of fatigue when she broke through at halfway and outstripped everyone to score.
The game was ended a few minutes early due to East Coast injuries - otherwise, a few more tries would likely have been scored.
But for coach Junior Nepia, the best news was that his squad is at full strength again after resting to some degree in the last couple of games.
“It’s great to see a couple of them – Te Amorangi [Karaitiana], Brookie [Brooklyn Walker], Keisha - back full-running.
“[We’re] still building for next week, but it was good to tick boxes, particularly around knowing we could use width.
“We’ve got the likes of Anahera and Samara, Hayley floating around out wide - if not to drag in numbers and punch holes, then to clean and support.”
That kind of performance was going to make it hard for the coach and his backroom staff to choose the squad for the championship final in Taupō on Saturday.
“We’ve got two to come back. De-Ann [Tyrell]’s our main one. Out of a squad of 26, we’ll have to go to 23, which is unfortunate.
“But they’re very much, 100 per cent, team-[focused], and we’ve talked to them about still having a role, still having a job. That doesn’t go away but, otherwise, it’s a great problem to have.”
While Whanganui were already locked into their final spot, they had to see who would join them, and the King Country Trailblazers emerged with a 37-27 win over the Thames Valley Vixens in Te Kūiti.
“We’d anticipated [playing] KC, just as a collective between myself and Maze [Koro]. We’ve watched a bit of their footage, so [there were] little bits and pieces that we wanted to try today that we thought would go a little bit further next week,” Nepia said.
Whanganui 79 (L Nepia 2, A Hamahona 2, K Campbell 2, K Mete-Renata 2, K Hunt, R Tamati, P Munro, H Gabriel, G Adams tries; A Ireton 5 con, Campbell 2 con) bt Ngāti Porou Hamoterangi 0. HT: 33-0.
