Southland Boys' came out on top with 50 points after the round robin, followed by Otago Boys' 47, King's 41 and Gore 40.
All points will be deleted for the new three-round competition and the top two teams will play off for the Highlanders First XV title.
The tenacious and strong-tackling Dunstan team kept the game scoreless until King's scored two converted tries in the last 10 minutes of the first half to lead 14-0 at the break.
The first went to substitute prop Asia Taana and the second to elusive first five-eighth Gifford Henry.
Kings dominated the scrum, made ground with the pick and go and was skilled at recycling.
Prop Ayden Lloyd was a strong scrummager and lock Connor Kemp won ball in the lineout.
The inside back combination of Caleb Gray and Henry created scoring opportunities but the strong Dunstan defence restricted King's to one second-half try by reserve winger Hayden Pringle.
The tenacious Dunstan team took its opportunities and scored 15 points in the second spell and came close to causing an upset when it camped within the King's 22m for the last 15 minutes.
Key players for Dunstan were flanker Keelan Baird, No 8 Nathan Huddleston and prop Lani Rooney.
Fullback Michael Lamont was strong on the counter-attack and the inside pairing of Tom Dougherty and Sean Conner was an efficient unit.
First five-eighth Scott Eade was the hero for unbeaten Southland Boys' when he slid through a gap to score the last try of the game and add the conversion to give his team a 21-16 win over Gore.
Gore was leading 16-14 when fulltime was up on the clock and looked like causing the big boilover of the competition.
Otago Boys' had a comfortable 62-24 win over Waitaki Boys' in the midweek game.
Dunstan finished fifth and heads the middle four with 28 points, followed by John McGlashan 27, Waitaki Boys' 24 and Verdon 23.
Verdon had a bonus-point 31-27 win over Kavanagh College.
Kavanagh scored four tries in a sparkling first spell to lead 22-12 at the break, but the strong Verdon forwards got on top in the second spell and the winning try came in the last five minutes.
Winger Joe Muasika scored three of the five Kavanagh tries, while the midfield of James Tomkinson and Guy Woodhouse was dangerous on attack.
Prop Mike Bennett was the best of the Kavanagh forwards.
The bottom four teams are South Otago 15 points, Kavanagh 14, Central Southland 12 and St Kevin's 5.
First five-eighth Quintine Gare scored two of South Otago's four tries when it outclassed Central Southland College 27-0 at Balclutha after leading 17-0 at halftime.
The other tries were scored by flankers Bryce Vreugdenhil and Johnny Fa'Amoe.
Players to impress for South Otago were winger Sylvester Reeves and tighthead prop Shane Edwards.
