They also retained the Hanan Shield, the Phil Gard and Bill Direen Memorial trophies.
However, Thames Valley ran rampant to score a 52-35 win over Mid Canterbury to remain right on South Canterbury's tail.
Whanganui knocked Horowhenua Kapiti out of third place when claiming a 40-15 win over the Levin-based side which led 15-14 at halftime but which was unable to score in the second half.
Horowhenua Kapiti remains in the top four as a result of North Otago and Mid Canterbury losing.
Poverty Bay moved into fifth position with a bonus point 50-26 win over King Couuntry, two points behind Horowhenua Kapiti.
East Coast thrived on the boost it received this week and ended its run of losses since 2013 by celebrating in style with a 50-26 win over Buller scoring seven tries in the process. They moved ahead of West Coast and into eighth place on the back of their win.
West Coast did pick up a bonus point, going down by one point 18-19 to Wairarapa Bush in Masterton.
Thames Valley 52 (Todd Doolan, Joe Cooke 2, Matty Axtens, Tevita Halafihi , Cameron Dromgool, Harry Lafituanai tries; Doolan 3 con, 3 pen; Telly Hemopo con) Mid Canterbury 35 (Tait Chisman, Callum Burrell, S Koroitamana 2, Lote Nasiga tries; T Reekie 5 con). HT: 32-21
East Coast 50 (Teina Potae, Sam Parkes 2, Te Rangi Fraser 2, Tawhao Stewart, Jack Richardson tries; Fraser 6 con, pen) Buller 26 (Iliesa Tora, Petrus de Kock 2, Mitieli Kaloudigibeci tries; Andrew Norton-Taylor 3 con). HT: 24-5
North Otago 27 (Mat Maui, Able Malalogo tries; Malalogo con, 5 pen) South Canterbury 33 (William Wright, Anthony Amato, B Sireli, Luke Glenn tries; Sam Briggs 2 con, 3 pen). HT: 11-8
Poverty Bay 50 (Kelvin Smith, Stefan Destounis 2, Tamanui Hill, Keanu Taumata, Toru Noanoa, Tione Hubbard, Riki Terekia tries; Smith 4 con, P Manuel-Harman con) King Country 26 (Sisa Vosaki, Bradly Jeffries, Kodi McGovern, Jesse Douglas tries; Johnny Ika 3 con)
Wairarapa Bush 19 (Lewis Bush, Vesi Luatua tries; Tipene Haira 2 pen; Moomoo Falaniko pen) West Coast 18 (Lewis Jackman, Jarrod Ferguson tries; Jacob Lowe con, 2 pen). HT: 16-7
Whanganui 40 (Semi Vodosese 2, Alekesio Vakarorogo, Dylan Gallien, Mathew Taula Fili, Dane Whale tries; Ethan Robinson 3 con; Dane Whale 2 con) Horowhenua 15 (Lennix Tovo, Bryn Gordon tries; Jackie Tatu-Robinsson con, pen). HT: 14-15