Flanker Alando Soakai celebrated his 50th game for Kaikorai with an aggressive and winning display to help Kaikorai lift the Frank Cadman Memorial Trophy at Bathgate Park.
Luke Herden was powerful in the Southern midfield and threatened the line every time he touched the ball.
He made the break for the first try when winger Greg Zampach used his speed to give Southern a 7-0 lead.
Kaikorai hit back late in the spell when centre Danny van der Voort broke out of his own 22m and No 8 Kensak Palepoi scored the first of his two tries.
Kaikorai led 11-10 at the break and extended the margin by seven points after two minutes when Palepoi scored his second try.
It looked to have the game safe when it led 25-10 after winger Richard Cowley broke out of his 22m and halfback Tomasi Palu was in support to score the try midway through the spell.
Herden brought Southern back into the game with a power-packed solo 30m run down the touch line when he pushed off tacklers to reduce the gap to eight points.
Another Herden break five minutes later led to a try by fullback Hamish Buick.
The Southern front row of Kees Meeuws, Ean Griffiths and Warren Moffat took control in the last 20 minutes and made ground with the pick and go.
The fleet-footed Julius Glasson added class to the backline as Southern almost pulled off a Houdini act to win the game.
Kaikorai 28 (Tomasi Palu, Kensak Palepoi 2 tries; Cam Rutherford 2 pen, con, Danny van der Voort pen, con), Southern 24 (Greg Zampach, Luke Herden, Hamish Buick tries; Lewis Hancock pen, 3 con).
Halftime: Kaikorai 11-10.
Referee: Tim Baker.
