The only YMP seven-pointer came from a penalty try in the first half, as they struggled to find space for their outside backs in the trying conditions.
OBM were able to build attacks with patient yet effective play through the middle of the park with the forwards, who imposed their will on the game.
They were led from the front by captain and hooker Rikki Terekia, who scored two tries in another outstanding performance as leader.
Centre John Jones scored the team's other two tries, finishing off two well-worked team moves.
OBM first five-eighth Jake Holmes was also outstanding, controlling the game brilliantly. He has blossomed as a player in the second half of this season. His decision-making and kicking ability in both open play and from the tee have been superb.
Going into the second half, OBM were ahead 20-10, but it wasn't clear if they would be able to maintain the intensity of the first 40 minutes. Manwhile, it would be interesting to see how YMP responded to the adversity.
YMP looked to speed up the game but were let down by their decision-making as they started to get desperate. One tap-and-go saw YMP penalised at the first ruck for immediately going off their feet; another was given away with a box kick on the second phase.
Their playmakers weren't able to find the space to work. OBM worked hard to shut them down and were successful in the tricky conditions.
The YMP forward pack played well, as did the players off the bench, but they weren't able to match the level of intensity OBM brought to the game.
OBM continued to pile on the points through slow build-ups of pressure that made YMP defend, wearing both them and the clock down.
Veterans of the team like winger Te Peehi Fairlie and Austin Brown tried to lead from the front, but the OBM defence was steadfast as YMP struggled to find front-foot ball.
With less than 20 minutes to go and needing more than three converted tries to retake the lead, YMP's frustrations started to boil over.
They saw two late yellow cards for dangerous tackles, to reserve flanker Shy Wyllie and centre Taine Aupori, with the game finishing in a scuffle.
OBM were convincing winners. With their full-strength forward pack for the first time against YMP this season and the wet conditions, they always had a chance. But such a convincing result will give them confidence that they can produce another heroic performance, this time against Waikohu, whom they beat in their first game of the season.
OBM coach Clint Pirihi said his team had a different energy in the build-up, and the warm-up was good, but he didn't expect them to dominate the game the way they did.
“I wanted to go back to the defensive structures we had in the first round.
“For us to dominate like that and keep them tryless . . . it was really surprising. I didn't expect us to be so strong through our forwards and backs on Saturday.”
Pirihi said they had focused on turning their defence into attack. The loose-forward trio of Morgan Reedy and flankers Hori Whakatopi and Keanu Taumata were crucial to the plan's success.
“They complemented each other all day. They played out of their skin.”
GT Shearing Waikohu put in a dominant performance, allowing Larsawn Ngatapa only a single penalty early in the second half of their semifinal.
They made a statement going into the final, winning their semifinal by 44 points.
Waikohu have been the team to beat all season, although OBM are the only team to have toppled them on their journey to a shot at winning the Lee Bros Shield in back-to-back years.
Ngatapa were unable to remedy their flaws from last Saturday, as they suffered their second defeat to Waikohu in as many weekends.
They were able to restrict the early scoring with some spirited defence, but the constant waves of attack started to erode their structure and resilience.
An inability to make forward progress with the ball against a staunch Waikohu side made attacking even harder, and Ngatapa struggled to enact their game plan.
Waikohu gained more and more metres as the game wore on. Their big forwards didn't seem to tire, even Jarryd Broughton, who was likely brought on earlier than desired after prop Tulsa Kaui was yellow-carded late in the first half.
Ngatapa did have periods where they were throwing bodies at the defence, but the Waikohu line held strong and eventually repelled them.
The ball handling was of a high quality from both teams, but Waikohu were able to use their width in the backs, despite the rainy conditions, to better effect.
Ngatapa head coach Stephen Hickey said they weren't able to match the intensity of Waikohu.
“We defended really well for the first 20 (minutes), but they were too good. There's nothing much more to say.”
YMP 10 (penalty try; Austin Brown penalty).
OBM 36 (Rikki Terekia 2, John Jones 2 tries; Jake Holmes 2 conversions, 4 penalties).
Halftime: 20-10 (OBM).
Ngatapa 3 (Ricardo Patricio penalty).
Waikohu 47 (Jessie Flemming 2, James Rutene, KC Wilson, Jacob Leaf, Tione Hubbard, Kupu Lloyd tries; Kelvin Smith 6 conversions).
HT: 19-0.
