Claiming a try-scoring bonus point in a 34-18 win over Ngāti Porou East Coast was enough for it to maintain that one-point lead over South Canterbury.
The southern side beat neighbour North Otago at Fairlie 36-17.
That left North Otago to share third place with Thames Valley who beat King Country 19-15, and Buller who got back up to the winner's circle to beat Poverty Bay 48-20.
Horowhenua Kapiti's 33-17 win over Wairarapa Bush in Masterton gave it sixth place with a Mid Canterbury side that kept West Coast scoreless in the second half while it ran in 40 unanswered points after being down 8-15 at the turn.
Bunnings Heartland Championship, Round Three
Buller 48 (Mitieli Kaloudigibeci 2, Michael Stringer 2, Isea Lewaqai, Iliesa Tora, Te Puoho Stephens tries; Jack Parker 5 con, pen) Poverty Bay 20 (Mitchell Purvis, Ted Walters, Jordan MacFarlane-Rofe tries; Moses Christie con, pen). HT: 29-10
Ngāti Porou East Coast 18 (Scorers not provided) Whanganui 34 (Aleki Vakarorogo, Tyler Rodgers, Gabrial Hakarai, Lindsay Horrocks, Semi Vodosese tries; Ezra Malo 2 con, pen; Ethan Robinson con). HT: 11-20
King Country 15 (Scorers not provided) Thames Valley 19 (Laulea Mau Fangufangu 2, Todd Doolan tries; Dooland 2 con). HT: 5-19
Mid Canterbury 48 (Isireli Masiwini, Michael Hennings, Kaydis Hona, Waitangi Tuisuga, Tyler Blackburn, Tom Reekie, Manasa Samo tries; Tom Middleton 4 con, pen; Tom Reekie con) West Coast 15 (Ben Wyness, Troy Tauwhare tries; Wyness con, pen). HT: 8-15
South Canterbury 36 (Kalivini Leatigaga 2, Siu Kakala, Zach McKay tries; Sam Briggs 2 con, 4 pen) North Otago 17 (Mona Somate, Paea Fifita, Sione Palaa tries; Josh Robertson Weepu con). HT: 13-5
Wairarapa Bush 17 (Aidan Champion, Tafa Tata tries; Aidan Champion con, pen; Ben Brooking con) Horowhenua Kapiti 33 (Tautau Kapea, Willie Paia'aua, Keaton Kawana tries; Jack Tatu-Robinson 3 con, 3 pen; Tyler Tane pen). HT: 3-16