Highlanders winger Lucky Mulipola scored a runaway try to complete Southern's comprehensive comeback win at Watson Park.
Down 10-0 at half-time, and fortunate not to trail by more, Southern lifted its intensity in the second spell during which it scored 24 unanswered points in 21 minutes.
Mulipola finished it off when Ciaran Fenton was hit in a heavy tackle and Mulipola scooped up the loose ball and sprinted 35m to score.
The damage had been done earlier when Southern, buoyed by a major territorial advantage, scored good tries by left winger Daryl Caldwell (after a fine break by replacement five-eighth Julius Glasson) and by Glasson himself after Luke Herden flicked him a neat reverse pass.
Glasson made a big difference after he took the field and his incisive running tested the Harbour defence and lifted his team-mates.
Simon Knight, son of Otago's most-capped player, Richard, had a most useful game from the blindside flank, gaining quality line-out ball and excelling in support play.
Harbour's Eben Joubert had a terrier-like game from the blindside flank until he was subbed, fellow flanker Jason Kelly was an honest worker from the other flank and the front row of Peter Mirrielees, Ben Nolan and Aaron Larsen anchored a sound scrum.
Southern 24 (Daryl Caldwell, Julius Glasson, Lucky Mulipola tries; Craig Sneddon 3 conversions, penalty goal), Harbour 10 (Henry Holdaway try; Ciaran Fenton conversion, penalty goal).
Half-time: Harbour 10-0.
Referee: Doug Rodgers.
