The visiting side trailed 4-0 through four innings but brought it back to 5-5 after the regulation seven innings.
Southland then got hold of Otago pitcher Ben Watts, running on fumes after a mammoth 150-pitch effort, to score three runs in the first inning of the tiebreaker, when teams start with a runner on second base.
Ryan Williams pulled a run back for Otago with an RBI single but it was not enough to reclaim the shield for the first time since 2009.
Otago had grabbed an early 1-0 lead when Jamie Robinson scored on an illegal pitch, and poured in three more runs in the fourth inning. Matt Watts hit an RBI single and scored on an error, and Williams also scored on an error.
But the good work was undone in the fifth inning when Southland piled on four runs to level the scores.
Chris Telfer, from the notable Southland sporting family, and Tim Campbell had RBI singles, and Jonathan Campbell added an RBI double to get Southland back in the game.
Otago regained the lead in the sixth, when Tane Tuhakaraina tripled and then scored, and was one out away from victory in the top of the seventh when Jonathan Campbell scored on an error.
There was a nervous moment when Southland loaded the bases, but Otago got out of the inning without further damage. Just as well, too, as Otago went three-up, three-down in its next bat to send the game to the tiebreaker.
Ellis Park snapped its drought with a 12-10 tiebreaker win over Cardinals in the premier club competition on Saturday.
Ryan Williams (Ellis Park) and Lyall Scott (Cardinals) hit early home runs as Cardinals built a 6-3 lead through three innings and held it until the top of the seventh.
Then things got a little crazy. Ellis Park scored six runs, the highlight another blast from Williams that scored three, and Cardinals made it 9-9 on Glenn Forrester's two-RBI homer.
Neither side could score in the first tiebreak inning, but a Simon Wallace triple keyed a three-run ninth inning that sealed Ellis Park's first win in eight attempts this season.
In the most even round of the season, each of the four clubs had a win and a loss.
Ellis Park had earlier fallen 5-3 to Dodgers, though it showed spirit to come back from a 5-0 deficit.
Saints, powered by triples to Tim Howard and Travis McIntosh, beat Dodgers 5-3.
Cardinals upset Saints 11-3. Saints had been up 3-1 before Cardinals roared back with an explosive third inning that featured home runs to Doug Hill, Mitchell Finnie and Crete Whaanga.
Jacob Wedlock also went long for Cardinals, in the fourth, while Scott capped the win in glorious fashion with a grand slam in the sixth.
