Otago Boys' got home after going out to a 23-6 lead early in the second half and managing to hang on as Marlborough came home hard, scoring two converted tries in the final quarter of the match.
Otago Boys' looked lively with the ball in hand and made some strong hits on defence.
Its scrum was solid and it could have won by more as it butchered a couple of golden opportunities in the first half.
Both teams traded penalties in the opening period.
The game was blown open just before halftime when Marlborough Boys fullback Mitch Smith attempted to move the ball on and it was intercepted by big Otago Boys' No 8 Tui Katoa. He ran unopposed to dot down under the posts.
Otago Boys' scored its second try seven minutes into the second half when flanker Matt Heffernan skipped clear after Marlborough had failed to clear a kick.
When impressive second five-eighth Sio Tomkinson kicked a penalty, Otago Boys' had a foot in the final.
Marlborough Boys' steamed back into the match through its big forwards but came up short.
Best for the home side was lock Brendan Murdoch and big props Jermaine Ainsley and Jonah Aoina. Tomkinson looked classy and fullback Reece Mau'u ran hard.
The assignment is a stiff one for Otago Boys' next weekend in Rotorua when it will take on St Kentigern College, from Auckland, which has not been beaten since 2011.
It beat Westlake Boys 65-8 in the Blues final on Saturday.
Dunstan High School lost 34-10 to Ashburton College in the South Island final for co-educational schools on Saturday in Ashburton. Dunstan was down just 11-10 at halftime.
Taieri College was beaten 76-7 in its promotion match for the Highlanders First XV competition against St Peter's College on Saturday.
The scores
OBHS v Marlborough Boys' College
Otago Boys 26
Tui Katoa, Matt Heffernan tries, Sio Tomkinson 2 con, 4 pen
Marlborough Boys 20
Bevan Moody, TC Campbell tries, Corey Bevan 2 con, Mitch Smith 2 pen
Halftime: 13-6 Otago Boys
