Hooker Damarus Hokianga scored a try and HBHS were also awarded a penalty try. First five-eighth Shamara Brooks kicked two penalties and a conversion.
Udy-Johns and Mataira were full of authority while locks Emil Crichton and Julian Goreke were a powerful pair.
Napier Boys High School were handed their first loss in the Super 8 competition on Saturday.
"We fell off a couple of tackles during key moments. There were two or three of those crucial moments and it's a learning thing for us," NBHS head coach Brendon Ratcliffe said after their 29-15 away loss to joint defending champions Hamilton Boys High School.
Halfback Treyah Kingi-Taukamo, a late replacement in the starting XV for Angus Kilmister, who was still struggling with a dislocated finger, performed well. Loosies, blindside flanker Josh Gimblett and No 8 Luke Russell, who are both in the Hurricanes under-18 squad, had huge workrates in the visiting pack.
"It was a really good contest. It was pretty close for most of the game and Hamilton scored a converted try on the last play of the game to blow the score out," Ratcliffe said.
"Our set piece went well. Once we get those key moments right we will match it with any team in the country," he added.
The score was 7-all at halftime and 22-15 to Hamilton before the last play of the game. Kingi-Taukamo and prop Patrick Teddy scored Napier's tries. Second five-eighth Keegan Christian-Goss kicked a conversion and a penalty.
This was Napier's first loss in four games while Hamilton remain unbeaten.