It was the key game in the top-eight round of the Highlanders First XV competition.
Otago Boys' led 7-0 at halftime but its defence was tested in the second spell when Southland Boys' held on to the ball for long periods.
Towering No 8 Tui Katoa scored a try and was the best of the Otago Boys' forwards. He was backed by lock George Latta and flanker Jamie Mowat.
Midfield back Sio Tomkinson scored the other try and kicked the conversion to give Otago Boys' the four points.
Ashley Craig scored the try for Southland Boys' which was was converted by Shaun Henderson. Jono Hayes kicked a late penalty goal.
Centre Chris O'Connell scored 22 points in John McGlashan College's eight-try, 52-8 romp over Menzies College in Dunedin. He scored two tries and kicked six conversions.
The McGlashan pack dominated the scrum, lineout and breakdown and set the platform for the fast backline, with winger Robert Jopp using his pace to score a try.
The other tries were scored by locks Stan South and Charlie Beckett, No 8 Nemo Gent, halfback Ed Davies and second five-eighth Ben Grant.
Dynamic openside flanker Jayden Willcock scored two tries and played a key role in King's High School's 36-12 win over South Otago in Balclutha.
King's led 17-7 at the break and then lifted its game to another level to dominate the second spell.
Other standout players were captain and hooker Joe Cairns-Thomson and centre Robert Peseta, who used his strength to score a try. The other King's tries were scored by prop Himiona Wilson and winger Taylor Haugh. First five-eighth Bradley Thomson kicked four conversions and a penalty.
Hooker Josh Turnbull scored one of South Otago's two tries. The other was scored and converted by winger Rory van Vugt.
Dunstan High School scored seven tries when it beat Waitaki Boys' High School 41-8 in Alexandra.
First five-eighth Logan Cornish scored two tries and the others went to props Joe Blaikie and Aiden Smith, midfield back Sam Galletly and wingers Lachie Edwards and Matt Schorer.
In bottom six games Verdon College beat Mt Aspiring College 11-10, newcomer St Peter's beat Gore 17-6 and St Kevin's beat James Hargest 31-10.
