In an enthralling contest featuring eight tries, Manawatu's bench proved the ultimate difference, first five Otere Black in particular doing a lot of damage.
Things weren't looking good early for Northland, trailing 17-0 after just 22 minutes.
Second-five Ngani Laumape scored Manawatu's first after they caught Northland short on numbers. Fullback Jason Emery provided a great offload to put the former Warrior over.
After a simple Sam Malcolm penalty, Manawatu captain Heiden Bedwell-Curtis crossed for a soft try.
Manawatu gained the tighthead in the scrum, then the number eight sold a big dummy and ran untouched to score.
Northland then went on a seven-minute blitz to give themselves a 19-17 halftime lead.
A stretch of pick-and-go's on Manawatu's line ended with debutant blindside flanker Michael Faleafa crashing over for a converted try.
Five minutes later, Northland scored the try of the match, going fron deep inside their own 22 to score.
Standout fullback Solomon Alaimalo, also on debut, made a huge break down the sideline and offloaded to ever-present openside flanker Kara Pryor, who in turn shifted it to centre Warren Dunn for the try.
Pryor was in the thick of the action again just two minutes later, this time threading a well-judged grubber through. Winger Jone Macilai recovered the ball and gave it to Faleafa for his second.
Moulds raved post-game about the efforts of Faleafa and Alaimalo.
"Faleafa was big on debut. Alaimalo had a great debut, he had an awesome game. He's got some real talent, that boy," he said.
Manawatu hit a penalty directly off the restart, but a converted try to reserve flanker Jack Ram and a Peter Breen penalty gave Northland a seven point lead with just 15 minutes to go.
However Black came to the fore, playing a major role in Manawatu's two game clinching tries.
Firstly, he put a cross-field kick inside the 22 to impressive winger Ambrose Curtis, who beat Macilai to score in the corner.
Black duly added the extras to tie the game up, but he wasn't finished yet, getting multiple touches in the build up to their bonus-point try.
Emery looked to have blown a try when he didn't pass when there was a three-on-one overlap, but had enough strength to crash over from close range to give Manawatu the seven point win.
Moulds said they've made great strides in the early stages of the competition, but there are some work-ons.
"From our pre-season games we've grown heaps, we gave ourselves every chance to win," he said.
"We'll look at the breakdown and securing our own ball. We need to make it a bit cleaner for the halfback, especially in the last period. It got a bit messy."
Northland take two bonus points travel to Auckland for their next Mitre 10 Cup match on Friday.
Manawatu 34 (Ngani Laumape, Heiden Bedwell-Curtis, Ambrose Curtis, Jason Emery tries; Sam Malcolm 2 con, 2 pen, Otere Black 2 con)
Northland 27 (Mike Faleafa 2, Warren Dunn, Jack Ram tries; Peter Breen 2 con, pen)
Halftime: 17-19
