Heat skipper Jess Jonassen sent the Thunder in at Allan Border Field and marshalled her bowlers to perfection as the visitors crashed to 7-69 before a record WBBL stand of 64 for the eighth wicket by Hannah Darlington (40no) and and Taneale Peschel (24no) got the Thunder to 7-133
The Heat polished off the runs in 15.2 overs for a nine-wicket win to set up a WBBL final showdown away against Melbourne Renegades at the MCG on Sunday.
India international Jemimah Rodrigues was dropped three times, two of them sitters, on her way to a skilled 43 off 30 deliveries before retiring hurt.. She combined with opener Georgia Redmayne (50no) to set up the run chase.
Rodrigues had injured her left wrist in the field and had to retire in the 10th over. She must be in some doubt for the final but Redmayne and Charli Knott (19no) both showcased the depth the Heat have.
Parsons, 21, earlier took 3-10 in three classy overs to set up the side's sixth win in a row.
Thunder opener Georgia Voll (20) was looking good ahead her former side before chopping on to the first ball of Nicola Hancock's spell.
Jonassen showed immediately why she was named in the WBBL team of the decade when she cleaned up Chamari Athapaththu with her first delivery, a beauty that drifted in and spun away.
Wicketkeeper Tahlia Wilson holed out to Parsons and the visitors stumbled to 3-51.
Parsons snared the big wicket of skipper Phoebe Litchfield (15) who was brilliantly caught by Jonassen at mid-off as she leapt high and snaffled a well hit drive above her head.
Parsons had two in the over when Georgia Adams skied one. Jonassen snared former Heat allrounder Sammy-Jo Johnson. At 7-69 the Thunder were in dire straits before Darlington and Peschel got the Thunder to a competitive total.
Both posted their career-best totals and unleashed an array of sixes and fours as the Heat bowlers dished up rubbish in the latter overs.
The stand broke the previous record of 60, also unbeaten, set by Lauren Ebsary and Piepa Cleary in 2018 for Perth Scorchers against Melbourne Renegades.
The Heat lost Grace Harris (7) stumped early after a wild heave to give Sam Bates her 20th wicket of the season. Redmayne and Rodrigues then ensured the hosts were able to cruise to victory