A defiant Kavanagh team used the breeze wisely to lead 13-10 at the break in the only game played in Dunedin.
It held the line for another 10 minutes in the second spell before it gave away an intercept try and the dam burst.
King's had chances in the first spell but the attack was too lateral and the backs made too many mistakes.
But in second spell, the forwards drove powerfully up the centre before letting the speedy backline do its job. King's scored nine tries in the game and seven came in the second half.
No 8 David Taua made some powerful driving runs with the ball in hand and scored three tries. Winger Josh McCombie used his pace to score two tries, and the best try of the game came from fullback Mackenzie Haugh, who ran the length of the field to score.
The best players for Kavanagh were the midfield combination of Soane Amato and Hemau Samason, halfback Matthew Martin, fullback Liam Eathorne and No 8 Nathan O'Brien.
Waitaki Boys' High School scored two late tries to beat Dunstan High School 25-12 in Oamaru.
Waitaki led 13-0 at the break but Dunstan came back strongly to close the gap to one point, 13-12, for 25 minutes in the second spell.
Waitaki then moved the ball wide and scored two late tries to get the bonus point, with speedy winger James Pillay scoring three tries.
The other try was scored by first five-eighth Kane McLaughlin, who made several strong breaks during the game.
Fullback Jamie Robb was dangerous on the counter-attack and flanker Jake Rhodes was always close to the ball.
The young Dunstan team was shell-shocked in the first spell, but came out fighting in the second spell, with first five-eighth Callum Wright and hooker Ryan Fulton both scoring tries.
Defending champion Otago Boys' High School took no prisoners in its 12-try romp over Gore High School, winning the game 73-6 in the Southland town.
The big Otago Boys' pack got on top from the start and monopolised possession. Lock Josh Dickson dominated the lineout and took 70% of the ball thrown in by Gore.
No 8 Alex Fitzgerald ran strongly with the ball in hand and flanker Troy Callander had a lively game.
Otago Boys' had speed in the backline, with midfield back Aleki Morris scoring three tries and fullback Sean Conner two.
First five-eighth Sam Ellis scored a try and kicked five conversions and a penalty.
In other games, South Otago High School beat St Kevin's College 39-17, Southland Boys' High School beat John McGlashan College 50-0, and newcomer James Hargest College drew with Menzies College 17-17.
