An outstanding fielding effort then saw Balmacewan bowled out for 76, in 19 overs.
Two outfield catches worthy of Classic Catch status helped turn the match for Kamo.
The first was a two-handed diving effort in the covers to Cam Gordon, and the second left even the umpires in awe after Kian Bird - a left hander - dived to his right and took the ball with one hand, centimetres off the ground.
Andre Luiten then mopped up the tail, taking three wickets for no runs off 7 balls.
Pace bowler Max Turner (2-8) and off spinner Sam Webb (2-10) also chipped in with wickets.
The match was played in windy conditions, with bowlers at the venue's eastern end struggling into a steady westerly breeze that gusted up to more than 40 knots.
Team manager and Kamo Intermediate School principal Paul Shepherd said it was a team effort and showed the belief the boys had in each other.
The team play Kings Prep (Auckland) and Hereworth School (Central Districts) today (Thursday).
On Friday, KIS plays Hutt International Boys School (Wellington).