Rotoiti snatched the crucial victory over Greerton when Logan Henry kicked a penalty late in the game.
Greerton led 10-0 after 10 minutes thanks to a try from flanker Dan Van den Berg and typically accurate goalkicking from Elliott Davies.
Rotoiti then took charge with first Chanse Perham scoring and a double from the powerful Abraham Tito giving the home side a 19-16 lead at halftime.
Barnstorming Chiefs prop Siegfried Fisi'ihoi crashed over from a scrum to increase the lead to 24-16 after 50 minutes before Gregory Banister and Richard Deed scored tries to put Greerton ahead 28-27 with 10 minutes remaining.
But with deafening home support Rotoiti rallied and seized their opportunity in the 77th minute when Henry calmly converted after his side was awarded a penalty due to a Greerton tackling error.
Greerton coach Kevin Lee was not too disheartened with the defeat and is focused on the next round of the competition.
"I think it was a fair result today as Rotoiti possibly had more of the possession," Lee said.
"We stuck in there and gave a good performance. I'm just relieved we have made it through.
"It was a difficult, hard fought game. It was so important that we got the win over Whaka so pressure was off us slightly. We still wanted the win, but it wasn't our game today."
It was just as tight in the scrap for the Division One top four places to join the bottom four Premier sides to form the new Premier Two division.
Western Bay clubs Rangiuru and Judea were in contention when play began on Saturday but both lost crucial games to miss out.
Rangiuru finished fifth after losing 34-15 to second-placed Poroporo while Judea have to settle for sixth after they went down 31-22 to top performing Ngongotaha.
Rangiuru and fourth-placed Marist St Michael's were equal on points but Marist are promoted up to Premier One as they won the clash between the teams in round six.
