Buller lead 17-0 at halftime and worked their way out to 27 points before the visitors came back with several tries, as it was the boot of Buller first-five James Lash which proved the difference in a personal haul of 17 points.
Wanganui's next opponent Thames Valley slotted into a share of second spot on points differential after their comfortable 42-13 win over East Coast in Ruatoria.
Thames Valley scored six tries to one and will approach their first home match with a bit of confidence.
After missing out on the Meads Cup playoffs last year, Mid Canterbury and their one test All Black Regan King signalled early intentions with a 34-5 disposal of Poverty Bay in Ashburton.
The Canterbrians ran away with it in the second half, as loose forward Seta Koroitamana scored two of his team's five tries, with first-five Jarred Percival getting another as part of a 14-point tally.
The closest game of the round was in Levin as Horowhenua-Kapiti won an arm wrestle with North Otago 22-19.
Down 6-3 at halftime, the home side out-scored their guests three tries to one, with James So'oialo bagging 12 points, but the goal kicking of Josh Buckham and Dan Lewis kept the southerners in with a chance of an important inter-island victory.
Results, August 26.
Thames Valley 42 (Hayden Wisnewski, Shaun Hill, Tyrone Keith, Alex Bradley, Jarred Bayliss, Matt Hart tries; Chris Doak 2 pen, 2 con; Jarrod Goodall con) bt East Coast 13 (Parekura Lalaga try; Chris Palmer 2 pen, con).
Horowhenua Kapiti 22 (Kalim Kelemete, Ethan Pollock, James So'oialo tries; So'oialo 2 con, pen) bt North Otago 19 (Lisala Halaeva try; Dan Lewis pen; Josh Buckham 3 pen, con). HT: 6-3 North Otago.
West Coast 17 (Todd Struthers, Rowan O'Gorman tries, penalty try) bt King Country 6 (Reece MacDonald 2 pen). HT: 7-3.
Mid Canterbury 34 (Seta Koroitamana 2, Maleli Sau, Jackson Donlan, Jarred Percival tries; Percival pen, 3 con) bt Poverty Bay 5 (Siosiua Moala try). HT: 5-5.
Wanganui 79 (Timoci Seruwalu 3, Lindsay Horrocks, Kaveni Dabenaise, Tremaine Gilbert, Fraser Hammond, Simon Dibben, Angus Middleton, Craig Clare tries; Clare 3 pen, 6 con; Dane Whale 4 con) bt Wairarapa Bush 7 (Nikora Ewe try; Tim Priest con). HT: 30-7.
Buller 27 (James Lash, Scott Neighbours, Blair McIlroy tries; Lash 2 pen, 3 con) bt South Canterbury 24 (JP Koen, Kieran Cole, Loni Tounohuni, Bill Logavatu tries; Willie Wright 2 con). HT: 17-0.