The win, along with a crucial bonus point, pushes Otago up into third place on the championship ladder, and it still has two games to play, one more than the other teams around it.
Otago sits on 21 points, with Southland one point behind and Hawkes Bay ahead on 24 points.
Hawkes Bay's last game is against unbeaten Wellington in Napier while Southland has to travel to Pukekohe to take on Counties-Manukau, which also doubles as a Ranfurly Shield challenge.
Tasman is more than likely to qualify top.
Otago plays Northland on Wednesday in Whangarei, and if it wins that match will go to second on the table. Its final game is against Auckland at Forsyth Barr Stadium this Sunday, and by kick-off it will have the advantage of knowing what exactly it has to do, if anything, to get a home semifinal.
The situation was not lost on Otago coach Tony Brown yesterday.
''Hawkes Bay and Southland have got a couple of tough games. If they do not get any points then we will be in a good position,'' he said.
But Brown is not counting his chickens too soon. Otago first must take on a Northland side which has been highly competitive all season, though it has only won one game.
''We've got a few bumps and bruises and the boys are still a bit tender. It is tough but we know what we we are in for. We have to prepare as well as we can and get the recovery right.''
The match against North Harbour on Saturday went in fits and starts, but Brown said he was more than satisfied to come away with a win and a bonus point.
''We wanted to play our game and use some width. By doing that we managed to create a couple of opportunities. The tries that we got were good team tries.''
Otago started the match well and after recycling the ball several times, Jayden Spence went through and stretched out to score after just two minutes.
Hayden Parker added the conversion and also kicked three penalties in the first half, although Harbour came back right on halftime when Francis Saili scored.
The match got scrappy in the second half but replacement hooker Sam Anderson-Heather scored after Otago had gone through the phases about halfway through the second half.
Gareth Evans scored the fourth try when TJ Ioane moved the ball wide and North Harbour ran out of numbers.
Evans, Lee Allan and Tom Franklin all played well in the Otago pack.
Winger Fa'asiu Fuatai went off with a sore shoulder and is out for a couple of weeks. Brown is likely to name his side to take on Northland today.
Wellington confirmed its status as the best side in the competition with a 38-16 thumping of Auckland, while Bay of Plenty was relegated from the premiership after its 28-25 loss to Waikato.
Yesterday, Canterbury came from 13-9 down at halftime to beat Counties-Manukau 38-23, and Tasman beat Taranaki 27-20.
ITM Cup
The scores
Otago 37
Jayden Spence, Tony Ensor, Sam Anderson-Heather, Gareth Evans tries; Hayden Parker 3 con, 3 pen, Peter Breen con
North Harbour 23
Francis Saili, Brenton Helleur tries; Jon Elrick 2 con, 3 pen
Halftime: Otago 23-13
