Dunstan found itself trailing 8-7 at the break, following a late try in the opening half by the visiting Taieri team.
Both sides had trouble cracking the other's defence in the second spell, before Dunstan No8 Beau Meehan crossed to give his side a 14-8 win.
Dunstan coach Garry Marsh felt his side played much rugby for very little reward.
``I think we just failed to hold on to the ball at critical times,'' he said.
``But Taieri were up very quick on defence which put a lot of pressure on our inside backs. We felt we were probably passing... under more pressure than we needed to be.
``But all credit to Taieri - they came to play, they really did.''
Taieri first five-eighth Bob Martin cut through a gap to set up Taieri's first try.
Earlier, Dunstan fullback Jack Ryan finished off a good team try for the home team.
Dunstan plays South Otago High School today which will be a big challenge.
South Otago beat Waitaki Boy's High School 32-21 in Oamaru on Saturday to consolidate third place on the competition standings.
It led Waitaki 19-14 at halftime. Loose forward Timothy Faamoe and lock Jesse Hutton shone for South Otago, while No8 Sione Kaufusi had a strong game for the home team.
In other games, King's High School routed Kavanagh College 117-0 at Kettle Park, while John McGlashan College dispatched St Kevin's College 68-3 in Oamaru. Both sides are unbeaten after six games.
Otago Boys' High School 2nd XV beat Mt Aspiring College 34-26 in Cromwell. It moves into fourth place with Waitaki dropping down one to fifth.
