In close, Border's flankers Angus Middleton and captain Cole Baldwin were good spoilers, frustrating Ngamatapouri, while out wide winger Isaiah Hooper was in good touch on defence and attack.
Fullback Nick Harding had a marquee game for his team with two tries in a 19 point haul, as his first try and that of first-five Grayson Tihema were stunning solo dashes from the midfield.
Lock Jack Hodges made the afternoon difficult for his opposite Shaq McKay.
Ngamatapouri's dangermen of centre Jim Seruwalu, second-five Samu Kubunavanua and Isireli Baleitavuku were always threatening, but often went more sideways than forward, and were a step behind the pace of Border's own islander import in Kaveni Dabonaise.
Border coach Justin Lock was a little annoyed at the team's execution in the early stages, where after setting themselves up well, the ball would go down right at the tip of the final thrust.
"We sort of turned up here and tried to play them at their game a little bit.
"The razzle dazzle - a lot of turnover."
Nonetheless, Border's continuity was there as they were close to full strength, with the exception of the late scratching of prop Tietie Tuimauga, and the five competition points were crucial with Dave Hoskin Carriers Marist looming in the last round robin match.
"That guarantees a home semi now. Good for the boys to know they'll be home in the next two weeks," said Lock.
For Ngamatapouri coach Richard Carson, it was another case of high risk style not always bringing reward.
"Silly mistakes, that's what happens.
"The boys realise, and they're starting to come right.
"It's a learning curve, we look forward to next year.
"Just lacking a bit of forward power at the moment."
While Ngamatapouri's backline would get the ball in hand and then look to break the line, Border's backs moved in deliberate directions, with Dabonaise and Harding trying to put winger Tom Symes over but just being denied.
Getting a penalty lineout close to the line, big Fijian lock Sekonaia Kalou claimed the ball and just dove through for 7-0.
Border kept trying cut out passes that led to intercepts and fumbles, while Ngamatapouri could not complete their one golden chance to score with first-five Te Tua Kemp broke the line but went away from the supporting Seruwalu, before his pass off the deck was lost.
Play stayed broken and messy until Tihema seized his chance, stepping through a midfield ruck and then turning on the gas to get around fullback Carlwyn Riddles and score.
Border felt they were starting to hit their stride at 14-0 after 30 minutes, but write off Ngamatapouri at your peril, as they put the ball through the hands to score back-to-back in the opposite corners.
First, from a 30m scrum after Border's forward pass, Seruwalu hit the gap and put Kubunavanua over at the flag, and then after the visitors kicked out on the full, Ngamatapouri worked forward again and reserve Villie Kuruyabaki got a great over-the-top pass to halfback Emosi Vucago, who linked with No8 Bryn Hudson and Baleitavuku to put Riddles to put over at the other sideline on halftime.
Border looked nervous as they kicked out on the full again to start the second stanza, but then Harding found something from nothing as he fielded a clearing kick and stepped past his chasers into Ngamatapouri's half, then backed himself to get around Riddles and dash away for 21-10.
Harding added a penalty for a 14-point buffer entering the final quarter, and while he missed another attempt to put the match out of reach, Ngamatapouri were being trapped in their own dangerzone and in their rare opportunities to get territory they soon gave away turnovers or lineout throws.
The home side were getting frustrated and conceeded a series of penalties, while Border put the screws on as they worked close to the line and eventually found the gap in the far corner for Harding to dive in.
There was enough time left for the home side to show what they can do as Border missed touch and Ngamatapouri's back reserves all dealt the ball between each other with one-handed offloads before Seruwalu took it and dragged three defenders over to score near fulltime.
Border 29 (N Harding 2, S Kalou, G Tihema tries; N Harding pen, 3 con) bt Ngamatapouri 15 (S Kubunavanua, C Riddles, J Seruwalu tries). HT: 14-10.