South Otago travelled to Oamaru and defeated the home side 18-13, with right winger Elliott Dodge scoring two tries for South Otago.
The visiting team led 5-3 at the break and was down 13-8 at one stage but fought back with two quick tries and held on to secure the win.
Despite the loss, Waitaki Boys remains at the top of the table, but South Otago has a chance to overtake the Oamaru school as it has a catch-up game against Gore on Wednesday.
That game was postponed last week because of adverse road conditions.
Two games were played at Carisbrook on Saturday.
Otago Boys enjoyed a good 62-10 win over Kavanagh, and Central Southland beat Kings 24-5.
Southland Boys had a 66-0 win over St Kevins, while Dunstan had a convincing 44-13 win over John McGlashan.
In Invercargill, Gore High beat Verdon 17-12.
