Marist dominated from the start and were rewarded with an excellent try after nine minutes.
The passage of play started 10 metres from their own line and involved 31 phases before prop Ben Couch crashed over wide out.
Martinborough first five Tim Priest narrowed the gap with a penalty, before Malatai Malatai crossed for the first try of his hat-trick, when he ran on to a lovely pass from first five Kieran Te Whare after a scrum from 20 metres.
Marist lock James Goodger showed all his skill and pace when he easily intercepted on the halfway to score under the posts to extend the lead to 19-3 on 27 minutes.
Martinborough were rewarded for some gutsy forward play two minutes later.
Halfback Max Hornblow took advantage of a big blindside from a five metre scrum and easily crossed for their only try and a halftime score of 19-10.
Priest failed to return in the second half with what he described as a "minor shoulder injury", and Martinborough missed his cool head and control.
An attempt to run the ball out from their own line resulted in Marist centre Micky Te Whare falling on a loose ball to bag the bonus point try in the 47th minute.
The match then degenerated into a messy affair until Malatai set alight the last five minutes.
The flying fullback ran on to a lovely pass from Micky Te Whare and stepped past one player to dot down behind the posts.
Then, with time almost up, his injection of pace on halfway was too much for the tired defence as he crossed to complete his hat-trick.
For Marist, Malatai again displayed the speed and trickery that should see him achieve representative honours this season.
Goodger was all class in his first match on his return from injury. He was ably supported by fellow lock Lawrence Titter, who had an outstanding all round game.
Martinborough openside flanker Chris Raymond was strong on defence, while No8 Joshua Hawkins gave his forwards plenty of go-forward with his strong runs.
Former Auckland Under-19 representative Sione Vaena was an interesting replacement for the second half. Apart from one barging run of about 30 metres, he looked short of fitness.
Pioneer had to work hard to beat Carterton in an entertaining match at Jeans St.
The home team had the better of the first half and led 11-3 at the break.
Carterton came out fired up for the second half and were rewarded with a converted try to Trent Hopwood and two Andrew Humberstone penalties for a 16-14 lead with 15 minutes to play.
Pioneer's never say die attitude was to the fore in the final five minutes as they scored a try and a penalty to wrap up the match 27-19.
Gladstone were far too good for East Coast at Whareama, running in six tries in a 34-5 victory.
Results
Greytown 34 (Byron Karaitiana try, con 4 pen, Raymond Oakly, Carlos Rimene, Nick Robertson tries) Eketahuna 10 Paul Tikomainaivalu try, Tom Meule con, pen)
Gladstone 34 (Cameron Hayton 2, Andrew McLean, Inia Katia, William Silvey, Richard Webby tries, William Silvey 2 con) East Coast 5 (Penalty Try)
Marist 38 (James Goodyear, Malatai Malatai, Ben Couch, Micky Te Whare tries; Keiran Te Whare 2 Con, Ben Wilson 2 Con) Martinborough 10 (Max Hornblow try, Tim Priest pen, con)
Pioneer 27 (Nikora Ewe, Himiona Haira tries, Joe Thompson 5 pens 1 con) Carterton 19 (Trent Hopwood try, Andrew Humberstone 4 pens 1 con)
