The visiting side retained the cup only after a last-minute try to replacement fullback Jayden Stoop locked the scores after Central had made most of the play in the match.
A draw was good enough for the holder to retain it. South Otago won 34-5 last year.
The match started with a hiss and a roar when Clyde-Earnscleugh hooker Angus Gibbens appeared from a ruck and ran 30m only to be cut down and penalised after he found himself isolated.
South Otago made the play for the next 20 minutes, picking up a penalty goal to Lawrence pivot Lance Taylor and a try soon after to No 8 Simon Grant, who was one of South Otago's standouts.
Central bounced back courtesy of a Danny King break which resulted in a penalty goal to Dylan Fletcher.
However, just before halftime South Otago extended its lead to 10 points thanks to a chip-and-chase try to centre Sam Wyber, albeit with a hint of a knock on.
Central fought back after the break with another penalty goal to Fletcher. Then Wakatipu's King used his explosive pace to out-flank his opposite and kick it ahead only for the ball to bobble and bounce into the arms of centre Nathan Reid to touch it down.
Fletcher missed a tough penalty chance soon after but it did not matter as his side put several phases together to allow wing Mark Te Whaiti to score.
Fletcher converted and it looked as though Central might hang on for the win at 18-13 with 17 minutes left to play.
But it let its guard down and South Otago took its chance by building phases and getting into the right area of the field.
The pressure eventually told and that was when Stoop sneaked down the blindside to cross in the corner with a minute to play. Cameron Johnson could not convert from out wide for the win, leaving the match a draw.
Upper Clutha lock Justin Carney was the pick of the Central forwards, while King had no-one to match him for pace on either side. Grant was by far South Otago's best on both attack and defence while Taylor looked good early but was replaced.
South Otago 18 (Simon Grant, Jayden Stoop tries; Lance Taylor 2 pens, con), Central Otago 18 (Nathan Reid, Mark Te Whaiti tries; Dylan Fletcher 2 pens, con). Halftime: 13-3.
