Leading 51-40 with a quarter to go, the home side all but had the game in the bag. However, instead of taking the foot off the gas it blew the lead out to 61-44 in the first 5min of the quarter to seal the derby match.
Steel goal shoot Jhaniele Fowler-Reid became the franchise's all-time leading scorer just 3min into the match, notching her 1248th goal for the side in just her 28th match to surpass Daneka Wipiiti.
Trailing 16-11 after the first quarter, the Taxtix introduced Bailey Mes into the match in an attempt to find more space against Karaka and Purvis.
After the Steel scored the first three goals of the second quarter, Tactix defender Jessica Moulds made a couple of big defensive plays to help her side again pull to within five.
However, the home side raced out to a double-digit lead a few minutes later, after scoring five straight on the back of Karaka and Purvis intercepts.
Karaka finished the match with four intercepts and seven deflections, while Purvis had one steal and seven deflections.
After leaving her starters to play the entire first game last week, Steel coach Janine Southby finally went to her bench to start the second half.
Goal attack Sophia Fenwick, who spent the past three years with the Tactix, replaced Te Paea Selby-Rickit, who had a decent match in just her second start at goal attack.
Fenwick had a shaky start, missing her first five shots and allowing the Tactix to go on a 6-0 run and close the deficit to 40-36 midway through the third quarter.
But Karaka again made a defensive stop to rebuff the Tactix rally and swing momentum back the way of the home side.
The Steel are away to the West Coast Fever next weekend, while the Tactix are away to the Central Pulse.
Southern Steel 68 (Jhaniele Fowler-Reid 56/60, Te Paea Selby-Rickit 8/11, Sophia Fenwick 4/11)
Mainland Tactix 54 (Mwai Kumwenda 34/38, Bailey Mes 17/24, Gemma Hazeldine 3/5)
Quarter scores: 1st, 16-11; 2nd, 32-25; 3rd, 51-40.
