Waitaki Boys beat Otago Boys 15-13 in Oamaru on Saturday, after leading 10-3 at the break, while in the other match, Southland Boys made no race of it against South Otago, winning 78-5 in Invercargill.
The results leave Southland Boys on nine points in the top four while Waitaki Boys and Otago Boys both sit on five points.
South Otago is out of the running for the final, having previously lost to Otago Boys.
Otago Boys will play Southland Boys in Dunedin this weekend, while Waitaki Boys has to travel to Balclutha to play South Otago.
In Oamaru, Waitaki Boys started well and went ahead through a try by blindside flanker Manu Taita.
Fullback Brad McKenzie added a conversion and then knocked over a penalty.
In the second half, Waitaki went ahead 15-3 after a good try by centre Goodwin Williamson, following a fine run by first five-eighth Miles Medlicott.
Otago Boys came storming back with tries from wingers Poamo Aiiloilo and Makisua Tanuvasa, adding to a penalty goal by Liam Edwards in the first half.
Edwards had another penalty attempt near the end to win the game, but it hit the post.
Medlicott had a fine game for Waitaki Boys, while outside him, Palavi Tahaafe ran hard.
In Invercargill in the sunshine, Southland Boys was too good for South Otago, which was missing two key players in Matt Faddes and Lee Allan.
Southland Boys No 8 Sam Winsloe had a fine game, bagging two tries, but the win was marred by lock Zane Neustroski being sent off for stomping.
If teams are tied on points after next week's games, the finalists will be decided on points differential.
In Dunedin, Dunstan ran away in the second half to beat Kings 38-5, after being up just 7-5 at the break, and remains unbeaten in the middle four of the Zero Fees-sponsored competition.
Backs Jayden Spence and Jayden Laws-McKay both scored two tries for Dunstan while winger Dan Fowler scored a try for Kings.
In the other game of the middle four, Gore beat Verdon 22-5 in Gore.
In the bottom four, Central Southland came back in the dying minutes to beat Kavanagh 16-14 in Dunedin.
John McGlashan had a great first half to lead St Kevins 35-5 in Oamaru, and withstood a brave comeback from the home team to win 38-24.
