Wing Bryce Heem also had an outstanding night, scoring two converted tries with lock Mark Burman adding the other.
All three tries were the fruit of sustained pressure as Northland stylishly unlocked Bay of Plenty's defence with superb ball control over numerous phases.
Bay of Plenty stayed in touch in the first half with a penalty by first five-eighth Daniel Waenga and a try by openside flanker Sam Cane after Northland muffed a restart.
But they never came to terms with the pace and precision of a Northland attack that frequently used cutbacks to change the point of attack to buckle their opponents' defence.
Munro stretched the lead out with two second half penalties with Waenga adding a second for Bay of Plenty.
Bay of Plenty came back into the game in the final 10 minutes as Northland, down to 14 men with the sin-binning of first five-eighth Ash Moeke, began to tire and scored their second try through wing Lelia Masaga who crashed over in the left corner to set up a tense finish for an excited home crowd.
The gap narrowed to seven when Bay of Plenty, enjoying dominance for the first time in the game, managed to get numbers wide to outflank the Northland defence and speedy substitute Toby Arnold scored another unconverted try.
The kickoff gave Northland the chance to put the ball upfield with two minutes to go and plant themselves in the Bay of Plenty half and they held on to record a win to be proud of.
Bay of Plenty, with a bonus point for losing within seven points now have 20 points while Northland move to 13.
- NZPA