Jasmine Garner (28 disposals, two goals) was typically brilliant for the Roos, who were negated early on Saturday before gradually working their way into a position of command and ultimately a 7.12 (54) to 4.5 (29) victory which moved them to 5-3.
Kearney's move into the middle after halftime, following an engrossing duel with rival skipper Erin Phillips in the first two terms, was pivotal in helping North take control.
"It's really handy having an Emma Kearney, who you can take from half-back and put her around the football," Kangaroos coach Darren Crocker said.
"It's a nice luxury to have.
"We felt in the first half there was a real disconnect between every line.
"We were leaking badly early in the first half but after halftime we absolutely corrected that.
"The game looked so much more the way we wanted it to look (in the second half)."
Behind the determined leadership of Phillips and Ange Foley, and reinforced by the return of spearhead Gemma Houghton - making a meteoric return from ankle syndesmosis surgery - Port looked switched on early.
The home side's terrific pressure created turnovers which, unlike previous rounds, they were able to score from, fashioning a five-point quarter-time lead.
Garner, who got the Roos' running game rolling in the second stanza, goaled inside the first 90 seconds upon resumption before ruck Emma King sidestepped Hannah Dunn and finished spectacularly.
The Power pinched back some of the momentum when debutant Lily Johnson slotted her first AFLW goal, six seconds out from halftime, before being mobbed by her teammates.
Kearney's move onto the ball after the main interval helped North finally get on top in clearances and inside-50s.
Irish-born centre-half-forward Vikki Wall, who shrugged off a first-half injury scare when she was accidentally sandwiched by Phillips and Zoe Savarirayan, looked dangerous after halftime as Port began running out of puff.
The fourth quarter was all North, with Alice O'Loughlin's second six-pointer putting an end to the Power's surge before best-on-ground Garner smoothly ran in her second to add some icing.
"North Melbourne are a very good side," Port coach Lauren Arnell said.
"They've had a number of years longer than us together and we were able to show what we were capable of for a bigger chunk of the game.
"We were able to really take it up to them for a half of footy - I am proud of that.
"We'll keep plugging away. We're starting to see some reward for effort but unfortunately not in the wins column."
