Buller are the only unbeaten side in the competition after five rounds.
South Canterbury are in second place three points back after taking a bonus point win over Poverty Bay.
One point further back are Horowhenua Kapiti, who will play Buller in Westport in round six, who beat Wairarapa Bush 12-9 in a tryless game in Levin.
Heartland results from round five games played on Saturday:
Poverty Bay 28 (Clayton Kiwara, Rico Gear, Murray Hewson, Travis Gooch tries; Kiwara 4 con) South Canterbury 32 (Paul Fifta, Tenari Saumani 2, Tom Dwyer tries; Jared Trevathan 3 con, 2 pen). HT: 14-20
Wanganui 44 (Rhema Sagotoe 2, Josh Hamilton, Zyon Hekenui, Bryn Hudson, Clive Stowers tries; Hekenui 4 con, 2 pen) East Coast 7 (Pamona Samupo try; Kris Palmer con). HT: 0-27
King Country 15 (James Ritchie, Whakataki Cunningham tries; Cunningham con, pen) West Coast 10 (Brad Houston try; Tim Priest con, pen). HT: 10-7
Horowhenua Kapiti 12 (Perry Hayman 4 pen) Wairarapa Bush 9 (Greg Mullany 3 pen). HT: 3-6
Thames Valley 15 (Jason Laurich, Blake Hill tries; Josh Turner con; David Harrison pen) North Otago 19 (Ralph Darling try; Ben Palmer con, 3 pen; Stephen Fenemore pen).
Mid Canterbury 19 (Seta Koroitamana, James Dampney tries; Murray Williams 3 pen) Buller 29 (Iliesa Ravudra, Penijamini Nabainivalu 2, Isei Lawaqai tries; James Lash 3 con, pen).