With most of the possession, Mangapai used quick set piece plays to break through the Maungakaramea defence and pile on a further five goals in the second and third quarters.
Maungakaramea managed to stem the flow in the final quarter of the match and were helped by a couple of Mangapai's shots hitting the post but the damage had already been done.
Whangārei Boys' High School were the other big winners over the weekend with an 8-0 drubbing of Bream Bay on Friday night.
The game started evenly in the first quarter, but the floodgates soon opened, and Bream Bay had no answer to the relentless WBHS attack.
In the women's competition, Whangārei Girls' High School secured second spot on a close competition table with a 5-1 win over Hikurangi.
Hikurangi held their own for the first quarter of the match and had the school side at 1-1, before two quick goals to WGHS in the second quarter swung the momentum in their favour.
Maungakaramea were able to leap frog Old Girls on the table by beating them 4-1 in the other match on Saturday.