In a match which didn't come to life until the second stanza, after the visitors led 9-6 at the break, Otago could not get across the line and failed to win any ascendancy at the breakdown.
Southland slowed the ball down at the ruck, killing opportunities for the home team to get some flow into its play.
Southland regained the Donald Stuart Memorial Shield with the win, and the only consolation for the home side was another bonus point.
Otago had a sniff when winger Ryan Shortland scored a try to get the side within four points with 10 minutes left, but Southland controlled many of the key moments and Otago found the defence too hard to break in the final stages.
Southland was gritty and its loose forwards got through plenty of work, while the scrum battle was fairly even.
Otago hooker Jason Macdonald had a stand-out match, though strangely he was substituted after 55 minutes.
Loose forward Adam Thomson got through plenty of work and first five-eighth Chris Noakes grew as the game went on.
Centre Brett Mather made a couple of good breaks and Shortland did the basics well.
Tim Boys had a strong game for the visitors from the openside flank and No 8 Hua Tamariki was not far behind.
In the backs, first five-eighth Robbie Robinson showed some nice touches, while fullback Mark Wells was steady.
Southland came out firing in the second half and went 10 points ahead after three minutes.
After several phases on attack, Robinson put a great ball inside to centre Kendrick Lynn, who went in under the posts.
Otago finally woke up after this, with second five-eighth Andrew Parata and Noakes making breaks that nearly resulted in tries.
Noakes finally knocked over a penalty as Otago won some reward for its period of dominance.
He added another penalty to edge Otago closer with 25 minutes left.
But the real back-breaker for the home side came with 18 minutes remaining, when lock Josh Bekhuis barged over from a ruck after a good run down the left wing by flanker Tim Boys.
The first half was a dour struggle with neither side hanging on to the ball for long.
Southland started well but coughed the ball up at vital times, though its forwards nearly rumbled over after a clever move at the front of the line-out.
Otago did gain some territory in the middle stages of the half.
Mather made a strong break but momentum was slowed by the Southland loose forwards, who were committed on the advantage line.
Otago failed to get enough quick ball to get its game going, but did manage to pilfer plenty of Southland line-out throws.
Robinson opened the scoring with an impressive penalty after seven minutes, banging the kick over from 48m out.
Otago immediately equalised, Noakes knocking over a simple chance from 30m out in front.
The first five put the home side in front after 25 following a Southland indiscretion in a ruck.
Southland came back and Robinson tied the scores up again with a second penalty then put his side ahead right on half-time. Tasman came from behind to beat North Harbour 19-15 in their match at Albany last night, NZPA reports.
The scores
Southland 26 (Kendrick Lynn, Josh Bekhuis tries; Robbie Robinson two conversions, four penalty goals)
Otago 19 (Ryan Shortland try; Chris Noakes conversion, four penalty goals) Half-time: 9-6 Southland.
Crowd: 7000.
• Tasman lived off scraps of possession and territory and trailed 15-6 with 23 minutes to go.
But their breakthrough came when blindside flanker Daniel Crichton made a clean break near the 22m line and set up fullback Robbie Malneek for a try. Tasman levelled the scores when reserve prop Tristan Moran crashed over in the corner, then a Matty James penalty in the 78th minute sealed the win for the visitors.
Result: Tasman 19 (Robbie Malneek, Tristan Moran tries; Andrew Goodman penalty goal, Matty James 2 penalty goals), North Harbour 15 (Michael Harris 5 penalty goals).
Half-time: 6-12.
