The home team was too clinical for the composite team, scoring four goals in a devastating opening half. Southern lost some poise in the second spell but managed to add a fifth goal when Theresa Dickson slapped in a deflection.
Classy striker Phoebe Steele opened the scoring with a fine strike from the top of the circle.
Moments later, Lucy Kitchin drilled another long-range shot into the back of the goal and Kate Morris and Dayna Holland also scored before the break.
Southern dominated possession and territory in the second spell but squandered several opportunities to go further ahead.
Coach Mark Stafford was pleased with his side's performance but said the team "lacked the same intensity" in the second half.
"We can't afford to do that against the better teams," he said.
Defending champion North Harbour had a surprise 3-1 loss to Auckland B yesterday and will be looking to make amends in its final pool game against Southern today.
Southern beat Auckland B 3-1 on Monday and will go into the crucial encounter feeling confident. Despite being top of pool A, Southern could slip to third in the pool if it loses today and Auckland B has a big win against Mid-South Canterbury.
In the national under-18 boys tournament in Palmerston North, Southern beat Manawatu 2-0.
Auckland is also undefeated in pool A and the two sides will meet today to sort out top billing.
