Otago Boys' High School rattled the cage but failed to prise open the door.
St Bede's College won the South Island secondary schools final for the fourth year in a row when it beat Otago Boys' 32-17 in front of a crowd of 2000 at Tahuna Park on Saturday.
The Christchurch school will represent the South Island in the top four competition in Rotorua next week.
"We knew it would be a tough game and they made us work hard," St Bede's captain Shayne Anderson said. "They were a completely different team to what we are used to in Canterbury."
Otago Boys' started aggressively. It dominated the lineout, had a solid scrum and was aggressive at the breakdown.
But dropped passes, wrong options and strong tackling by St Bede's kept the line intact.
The turning point in the game came after 26 minutes, when St Bede's winger Moses Faletolu intercepted at halfway and dashed 50m to score the first try.
That sparked the St Bede's team into action and four minutes later its pack put five phases together inside the 22m before prop Jack Best crashed over.
The best player on the paddock was St Bede's fullback Yoshikazu Fujita (17), from Japan.
He was dangerous on the counterattack and was prepared to initiate attacks from any part of the paddock.
He followed up a clearing kick just before the break, grabbed the ball and sprinted 50m for the try.
His clever running from inside his own 22m led to his side's fourth try, when lock Misimoa Lamositele crashed over.
Tries to hooker Junior Pole and captain Michael Collins brought Otago Boys' back into contention.
St Bede's led 20-17 with 12 minutes left, but lifted its game to a higher level to score two late tries and win the game.
Otago Boys' hooker Junior Pole and Lachlan Landels were strong in the front row. No 8 Brodie Hume and lock Mike McKee tackled their hearts out and made strong runs with the ball in hand.
Josh Dickson won clean lineout ball when he came on in the second spell.
The scores
First XV final
• St Bede's 32
Yoshikazu Fujita, Moses Faletolu, Jesse Bryant, Misimoa Lamositele, Jack Best tries; Hagen Schulte 2 con, drop goal
• Otago Boys' 17
Michael Collins, Junior Pole tries; Sam Ellis 2 con, pen
• Halftime: 17-3.