The win will have restored some confidence following last weekend's 42-20 loss to Northland in Whangarei.
Experienced fullback Sheree Hume made many timely entries into the backline .
Centre Cheyenne Cunningham made some massive hits in the midfield, and Georgia Cormick provided quality delivery from halfback.
First five Maia Joseph steered the team around nicely.
Up front Miles led the charge with a typically energetic effort on the openside and prop Eilis Doyle brought some physicality.
Coach Craig Sneddon was pleased, particularly with the effort in the second half.
''Obviously we left a couple of points out there but that was definitely a big improvement for us,'' he said.
''It was all about intent this week and trying to score some nice tries.''
North Harbour struck early. An Otago mistake at the back presented them with a 5m scrum.
They hammered away and first five Grace Freeman spun out of a tackle and slipped over from close range in the 5th minute.
Otago was showing plenty of enterprise, though. They replied with a penalty through Cormick.
They should have got some more reward shortly after, but a combination of good defence and sloppy handling denied them further points.
Midway through the half the Spirit launched a series of raids at the line. They swung it left and right and back again.
North Harbour's defence held firm until Miles crashed over from a 5m lineout drive.
Otago got back into position to score after Hume skipped through in the midfield and found Cormick, who found Joseph and she got a nice pass to left winger Jamie Church, who galloped towards the corner.
The cover defence got her but hooker Tegan Hollows drove over from a lineout drive shortly after.
North Harbour's pack tried to regain some initiative late in the half with a maul which rolled forward 20m.
But Otago held on to take a 13-5 lead into the break.
The home team started the second stanza in style. Hume got through a half gap out wide and shovelled it to Church and won the race to the corner.
Freeman nabbed her second try when she took a quick tap penalty and strolled over.
Truth be told Otago should have done better there.
But they finished nicely with tries to Charlotte Va'afusuaga and Cunningham.
The scores
Otago Spirit 37 (Leah Miles, Tegan Hollows, Jamie Church, Sheree Hume, Charlotte Va'afusuaga, Cheyenne Cunningham tries; Georgia Cormick con, pen, Hume con.)
North Harbour Hibiscus 12 (Grace Freeman 2 tries; Freeman con.)
Halftime: 13-5
