Because Whanganui and Mid Canterbury had been part of a four-way tie for fourth spot last week, Whanganui's points differential gave them preference, but now with just two tied up, the Cantabrians hold the place due to winning the September 25 game between the sides.
The other two teams, North Otago and Poverty Bay, played out an extremely tight match in Oamaru, with the home side surviving 12-10.
All the other favourites picked up victories last Saturday, although each of the games was competitive.
South Canterbury continue to head the table after travelling up to Ruatoria and pulling away in the second half for a 34-12 win.
Likewise undefeated, Thames Valley made the long trip to the South Island and came away with a tight 27-8 win over West Coast in Greymouth - missing a bonus point to let South Canterbury take the outright lead.
Also travelling south were Whanganui's upcoming opponents Horowhenua-Kapiti, who kept their unbeaten streak intact with a 27-12 win over Buller in Westport.
Both sides scored two tries, but again the goal kicking of Jack Tatu-Robinson was crucial, which Whanganui must be wary of in defending the Bruce Steel Memorial Cup tomorrow.
Round 4 results, October 10
Horowhenua Kapiti 27 (Daniel Smith, Bryn Gordon tries; Jack Tatu-Robinson 5 pen, con) bt Buller 12 (Erenimo Tau, Mitieli Kaludigibeci tries; Jesse Pitman Joass con). HT: 16-0.
South Canterbury 34 (James Hawkey, Junio Faavae, John Borland, Vaka Taelaga, Zack Saunders, Siu Kakala tries; Sam Briggs 2 con) bt East Coast 12 (Tawhao Stewart, Te Wehi Wright tries; Te Rangi Fraser con) HT: 12-5.
North Otago 12 (Charles Elton, Tony Taufa tries; Josh Phipps con) bt Poverty Bay 10 (Jarryd Broughton try; Andrew Tauatevalu pen, con). HT: 7-3.
Thames Valley 27 (Ben Bonnar, Fred Kei, Will Newbold tries; Carlos Price 2 pen, 3 con) bt West Coast 8 (Troy Tauwhare try; Sean McClure pen) HT: 13-3.
Mid Canterbury 28 (Manasa Bari, Tom Reekie, Raitube Vasurakuta, Seta Koroitamana tries; Reekie 2 pen, con) bt Wairarapa Bush 18 (Lewis Bush, Ueta Tufuga tries; Moomoo Falaniko 2 pen, con) HT: 15-7 Wairarapa Bush.
Whanganui 48 (Peceli Malanicagi, Semi Vodosese, Kieran Hussey, Dane Whale, Aleksio Vakarorogo, Kameli Kuruyabaki, Timoci Serewalu tries; Ethan Robinson pen, 3 con, Dane Whale 2 con) bt King Country 13 (Bradly Jeffries try; Sio Tapili 2 pen, con). HT: 15-6.