Kamo came out firing with the bat as Onerahi's fielding effort let them down in a big way.
Openers Rhyce Brittain-Clark and Mark Donegan made their opposition pay for early lives as they cruised towards half-centuries.
Brittain-Clark was the first to fall with the score at 95 after making his way to 55.
Donegan (73) continued to thrive at Kamo Recreation Ground, hitting five boundaries and a trio of sixes as he and Jacob Cherrington (38 not out) guided Kamo home with 16 overs to spare.
Meanwhile WBHS showed they are a team to keep a close eye on after getting a tight win over Kaipara Flats.
Kaipara Flats decided to bat first at home and while plenty of batters made starts, continuity was an issue because no one could kick on.
Five batsman scored between 22 and 34 because they couldn't get on top of a determined WBHS bowling outfit.
Former Black Cap James Marshall top scored for the home side with 34 but it was spinner Lewis Miller who was the star of the show, returning figures of 5 for 32 from his 10 overs.
Kaipara Flats batted out the overs to end at 166 for 9, leaving a tricky chase for the visitors.
WBHS started tentatively as bowlers Shaun Beamish (2 for 25) and Ewen Thompson (4 for 41) piled the pressure on from the outset.
However Sean Sweeney (32) and Isaac Osbaldiston (48 not out) led them home in a top effort from the high-school outfit.
City meanwhile bounced back from a disappointing loss to cruise home against Maungakaramea.
Simon Fenwick (38) got City's innings off to a quick start with an enterprising 21-ball knock but Maungakaramea kept them honest through opening bowler Ian Wallace (3 for 51).
Joey Yovich (47) and Harry Darkins rattled off an important 96-run partnership to steer City towards 300.
However Maungakaramea bowled well late to keep City to 277 for 7, Darkins ending unbeaten on 103.
In reply Maungakaramea found runs tough to come by as City applied the breaks early.
Yovich (2 for 26) was the pick of the bowlers as everyone did their job well.
Sam Murphy was a shining light for Maungakaramea but was cruelly denied a century when Darkins ran him out on 98.
Maungakaramea batted out their overs but their 174 for 7 wasn't close to hitting the mark City set.