The Heat held their nerve to restrict a desperate Sixers batting line-up to 7-122, with pace bowler Nicola Hancock staring down the Sydney batting guns to claim 2-27 and spinners Amelia Kerr and Grace Harris claiming key wickets.
Kerr trapped Sixers batting trump Ellyse Perry leg before wicket after Hancock had removed the hard-hitting Alyssa Healy (29) with a subtle change of pace.
Harris nabbed a direct hit run out to remove Erin Burns (2) before snapping up Marizanne Kapp to a neat catch behind from Georgia Redmayne. The Sixers had stumbled from 0-41 to 4-71 in a matter of overs and had to rely on some counterattack from Dane Van Niekirk (31) and Angela Reakes (24no) to lift them to their total.
Harris finished with 2-13 from three overs while Kerr had 1-16 from four overs.
The Heat were forced to work for their runs, but captain Jess Jonassen (34) found willing partners in the impressive Georgia Voll (19 off 16), Maddy Green (18 off 21) and some outrageous hitting from Laura Kimmince.
Kimmince smashed 23 from nine balls, including a thumping six into the grandstands and a splendid reverse ramp shot from a full toss that just cleared her head on the way to a four.
Brisbane will now look to stay on a roll when they back-up tomorrow morning to tackle the Perth Scorchers at Hurstville Oval, traditionally a high scoring venue.
The Scorchers lost this afternoon to the competition-leading Melbourne Stars which have cleared out to be five points clear of the second-placed Heat.