Captain and halback Zane Hiko kicked a penalty for Tapuae, then opened the scoring in the second half with another penalty.
Soon after, Tapuae were down to 14 players when one of their props was sent off.
“The red card really fired the boys up,” Tapuae coach Wayne Hema said.
Second five-eighth Sean Hiroki scored Tapuae’s try soon after that to make it 11-6, then replacement first-five Carlos Carol kicked another penalty to complete their scoring.
YMP halfback Nathan Tamatea scored their try in the corner with five minutes to go to set up a gripping finish.
Hema said changes made in the second half paid off for them.
“Despite that late try by YMP, our team still had the goods, and we managed to hold YMP in their own half until the final whistle. The boys were pretty ecstatic about the win. They were over the moon and I was certainly happy we got that title.
“We are looking to move up to premiers next year and this result reinforces that desire.”
Hema said Hiko directed their play really well and No.8 Andre Mitchell was their player of the day.
“Andre’s overall game was tremendous. He secured a lot of crucial turnover ball when it was needed, and he carried the ball strongly.”
Bumbles coach Ron Tamatea named No.8 Dan Taituha their man of the match.
“Dan is very much an impact player and he played like that for the whole match.
“John Matenga in the mifield also had a good game.”
The generalship of Bumbles first five-eighth Waiti Tamatea was up to its usual high standard.
“A lot of the boys had not made a final before and big ups to them for getting there,” coach Tamatea said.
“If you look at where we came from at the start of the season, where we were not certain of having a team, to have made the final is a credit to the boys.
“It is very much something to build on for next year and the boys are excited about it.
“Congratulations to Tapuae. At the end of the day, it is all about the last game of the season, and they won it.”
As to their name the Bumbles — “It was a YMP team back in the 1970s, a social team,” said Ron Tamatea. “We just resurrected the name because I liked the sound of it and it gave us a bit of identity.”
Tapuae second five-eighth Sean Hiroki was named player of the final.