The eight-strong Otago team beat Canterbury 5-3 in a mixture of cadet, youth, and elite mens bouts.
The win means Otago claimed the inaugural "challenge belt", put up for the tournament by the Canterbury Boxing Association.
Otago Boxing Association president Colin Falloon said the win was a "huge achievement".
"On a national scale, Canterbury is a boxing powerhouse, so to beat them in their own backyard ranks right up in terms of achievements."
The tournament was the first of its kind since the association was re-formed in 2005, and as far as Falloon was aware it could be the first since 1952.
He said the hard work done by the association's former president, the late Tommy Trinder, was starting to pay dividends.
Otago started strongly when Aaron Lay won his lightweight cadet bout against Jayden Morgen (13-5). The 10-year-old backed the win up later in the day with a non-tournament win against Bryce Hearn, of Temuka, (10-7).
Canterbury jumped out to a 2-1 lead before Otago's female youth competitor, Siraya Wilson, evened up the score with a dominant win over Cheyenne Peck (24-9).
Falloon said Wilson (17) got out to a 16-4 lead going into the third round and although Peck did well to come back, the result was never in doubt.
Otago then took a 3-2 lead when lightweight youth Matt Crawford beat Rendall Remansese (13-6).
The heat went on Sam Beck (16) as he stepped up from his usual welterweight category and into the middleweight section.
Beck led 6-1 going into the final round but Canterbury's Chris Haxell got back into the fight, gaining an 8-8 draw. Beck eventually won on a countback.
With a 4-2 lead, and knowing the worst Otago could do was draw, it was up to Mathew Eaden to make sure the challenge belt headed down south.
The 22-year-old Eaden sneaked home in his heavyweight contest against Adrian Rock (8-7).
Trailing 1-0 after the first round Falloon said Eaden controlled the second and led 5-2 going into the third.
With Otago holding an unassailable 5-2 lead the final fight had only pride on the line.
Sergio Laishenko took on Sam Watt in an elite men's super heavyweight bout.
Watts' experience of 22 fights compared to Laishenko's four proved too big a hurdle for the 22-year-old Ukrainian-born fighter, Watts winning 15-1.
Laishenko and Lay are members of the Gore boxing club, coached by Russell Newton.
They were allowed to box for Otago after other match-ups fell through.
In other fights, Devlin Cook (Canterbury) beat Alex Hannan, and Kaelan Boyce (Canterbury) beat Awatea Henry.
Otago boxers will now turn their attention to a tournament in Ashburton in two weeks, before returning to Christchurch for the Canterbury Boxing Association championships on August 25.
Falloon said most boxers' main goal for the year was to compete in the New Zealand amateur championships in Auckland in October.
