Mossburn beat last year's beaten finalist Invercargill St Mary's 53-42. Mossburn made a nervous start to the match before pulling out to a 30-21 lead at half time.
Goal attack Selina Copeland, who shot 41 goals, was player of day. She was well supported by Rachael Dawson.
Mossburn coach Lynne Stevenson said St Mary's beat his side by 20 goals last year, so it was a good scalp.
"We have a lot of new and younger players this year and we are still getting to know each and establish links.
"Millie Walker (16) is a versatile attack player, learning plenty from our team leaders, Southern Steel defender Abbie Erwood and her twin sister, Sophie, at centre."
Defending champion Gore Ex-High beat Central Southland College 60-20.
CSC coach Andrea Beggs said the girls knew it was going to be a huge challenge against the top team first up.
"We are the new team in the competition this year, so concentrating on some team goals was the focus for this game."
CSC's standout players were centre Riley Ballantyne and Della May McDermott at goal keep.
Rata beat St Marys Gore 50-27, thanks mainly to a standout defensive team performance. Laura Overton and Georgia Dowling earned multiple turnovers in the defensive circle.
Rata coach Debbie Munro said the second quarter was huge.
"This was the quarter we really took off and scored 17 goals to one. It was a great all-round team effort."
Last year's semifinalist, Winton, beat Southland Girls High School 50-39. Winton was up by 16 at three-quarter time and was disappointed to let SGHS win the final quarter by five goals.
-By John Langford
