Marist held their 5-0 advantage well into the second half, thanks to a try from hooker Jack Yarrall.
Taihape flirted with surrendering the Grand Hotel Challenge Shield in their first defence before pulling away with three tries, although they missed the bonus point to lose their share of the points table lead.
Utility back Tyler Rogers-Holden scored a double, while loose forward Beau Walker also dotted down.
Taihape will come back to Whanganui this weekend to meet a slipping Wanganui Car Centre Kaierau, who are secure in third spot but can advance no higher, after a 44-7 drubbing from Border at the Country Club.
Scoring early and working their way up to 25-0 by halftime, Border were well on their way to a bonus-point win and moving clear of Taihape on top after surrendering the Shield to them.
After he missed out for the first time this season at Memorial Park, Vereniki Tikoisolomone was back in lethal mode with a hat-trick of tries, taking him to 18 from nine games.
Fellow outside backs Tom Symes and Ben Aitken got on the sheet, while No 8 Semi Vodosese scored in consecutive games.
Craig Clare may still be thinking about whether to give Heartland rugby one more go, but it would appear there is little to think about after a 12-point haul.
Kaierau received a seven-point penalty try in the second half, but that was all they had to show, having now lost three straight games for the first time since 2017.
Speirs Food Marton have no chance of making the Tasman Tanning Senior playoffs, but they caused another boilover with a 24-22 upset of Ali Arc Logistics - DNA Kennels Marist Celtic.
Celtic's shock loss means they could go from 2020 finalists to missing the playoffs altogether, as they host the undefeated Kelso Hunterville at home this coming weekend.
Hunterville were made to work by the Marist Buffalos at their domain, but eventually pulled away for a 29-6 win, guaranteeing they will finish top of the table.
Harvey Round Motors Ratana's focus is on keeping their home semifinal spot, which they did with a 36-6 win over McCrea Scanning Counties at McNab Domain.
Gemini Pepper Construction Kaierau beat Utiku Old Boys 28-17 at the Country Club.
It was sudden death for the playoff hopes of two teams at Memorial Park and Black Bull Liquor Pirates emerged with their most important win in two seasons, after coming from behind at halftime to beat Bennett's Taihape 35-27.
But perhaps the most emotional win was at Rochfort Park, as the Ruapehu Seniors delivered their eulogy for beloved co-coach Mark Green, rising to the moment to beat Border 53-5, just four days after they lost him in tragic circumstances.
Results, June 26
Tasman Tanning Premier, Week 9
Grand Hotel Challenge Shield – Byford's Readimix Taihape 17 (Tyler Rogers-Holden 2, Beau Walker tries; Dane Whale con) bt Dave Hoskin Carriers Marist 5 (Jack Yarrall try). HT: 5-0 Marist.
Waverley Harvesting Border 44 (Vereniki Tikoisolomone 3, Tom Symes, Ben Aitken, Semi Vodosese, Craig Clare tries; Clare pen, 2 con, Nick Harding con) bt Wanganui Car Centre Kaierau 7 (penalty try). HT: 25-0.
McCarthy's Transport Ruapehu 34 (Raymond Tutauha 2, Taina Wallace, Campbell Hart, Cyrus Tasi tries; Royce Trow pen, 3 con) bt Settlers Honey Ngamatapouri 27 (Jim Seruwalu 2, Josaia Dawai, Joeli Racau, Mairangi Tamehana tries; Te Rau Wirihana con). HT: 10-5.
Senior Championship, Week 10
At Kaierau Country Club: Gemini Pepper Construction Kaierau bt Utiku OB 28-17. HT: 18-5.
At McNab Domain: Harvey Round Motors Ratana bt McCrea Scanning Counties 36-6. HT: 12-6.
At Marton Park (Stihl Shop Wanganui Challenge Shield): Speirs Food Marton bt Ali Arc Logistics- DNA Kennels Marist Celtic 24-22. HT: 17-12.
At Hunterville Domain: Kelso Hunterville bt Marist Buffalo's 29-6. HT: 16-6.
At Memorial Park: Black Bull Liquor Pirates bt Bennett's Taihape 35-27. HT: 17-14 Taihape
At Rochfort Park: Ruapehu bt Border 53-5. HT: 38-0.
Around the grounds
METRO: It was a slightly tougher challenge at Ongley Park on Saturday, but St Johns Whanganui Metro kept their 10-match MRU Colts winning streak alive with a 42-11 win over Old Boys Marist. Metro will take their bye this coming weekend before the last regular-season game.
COLLEGIATE: Whanganui Collegiate 1st XV maintained third spot in the CNI standings after hammering St John's Hastings 56-10 at the school grounds on Saturday. Their next competition game is not until July 24, but will be a battle against defending co-champions St Paul's Collegiate.
SCHOOLBOYS: The Whanganui High and City College 1st XVs still occupy the top two spots on the MRU Premier 2 table, although neither won on Saturday. WHS were held to a 12-12 draw away to third-placed Horowhenua College, while City were just pipped by home side Feilding High 2nd XV, 20-19. In Premier 3a, Whanganui Collegiate 2nd XV lost 27-22 to Manukura 2nd XV.
