Midlands controlled the first half and went into the break leading 3-0 after goals from Kate Savory, Shiloh Gloyn and Natasha Fitzsimons.
Auckland lifted in the second half and pulled one goal back through Julia King in the 49th minute, but it was too late to salvage the game.
North Harbour and Auckland will play for the Ford National Hockey League bronze medal at 9am on Sunday.
The men's and women's bronze and gold medal matches will be live streamed on the Hockey New Zealand Facebook page, and in full high definition on YouTube.
The women's 5th/6th playoff will see the Canterbury Cats go up against the Central Mysticks with Capital and the Southern Storm playing to avoid the wooden spoon.
Canterbury powered past Southern 7-1 thanks to a four goal bag from Rachel McCann while Margot Willis added a hat-trick of her own.
The Central Mysticks secured a 3-1 win over hosts Capital in a shoot-out after going into fulltime with the score drawn 1-1.
Men's teams will play their semifinals and classification matches from 10.15am tomorrow ahead of finals day for all teams on Sunday.