The pressure compounded for the home side when halfback Te Ra Whata was shown a yellow card for some dirty play two minutes later.
It meant Rotorua, who were leading 29-27 at the time, had to hold on for the last three or four minutes with only 13 men.
They did more than that though, scoring a try right at the death. After the try, Boys' High fans ran onto the field to celebrate with their champions but were quickly told to get off the pitch so Kaleb Trask could take the conversion.
Trask slotted the conversion to make it 36-27 and the fans ran onto the field a second time as the final whistle blew.
The victory was the first national title for Rotorua Boys' 1st XV since 2003.