The form player of the tournament over the past fortnight, Mooney hit 76 from 44 balls for the Scorchers in Thursday night's preliminary final to set up a date with Hobart.
Set 184 to win at North Sydney Oval, the Sixers started strong before Alana King took 3-17 from four overs to rip the heart out of the chase.
And while the Sixers needed 20 from the final over, Lilly Mills held her nerve to ensure the Scorchers' passage to the grand final and end the Sixers' season.
Ranked the No.1 batter in the world in T20 cricket for large parts of the past five years, Mooney's form could well decide Saturday's final in Hobart.
After hitting 75 against the Hurricanes a fortnight ago, the left-hander put the Scorchers into the finals with 94no in a must-win clash with Brisbane last week.
She then backed that up with 45 in Tuesday night's knockout final against the Melbourne Stars in Perth, before again proving the difference on Thursday.
Offered a life on nine when Alyssa Healy fumbled a stumping chance, Mooney made the Sixers pay with the second-highest score in a WBBL finals match.
Mooney hit 12 boundaries and brought up her half-century off 27 deliveries, striking the ball crisply square of the wicket with a flurry of pulls, sweeps and cut shots.
She is now the leading run-scorer for the tournament, having passed 400 runs in 10 of the 11 seasons of the WBBL and reaching 386 runs in the other.
"I'm pretty lucky I get to open the batting and face a lot of balls," Mooney said.
"I've had a lot of help along the way, a lot of conversations with different coaches and a lot of people throwing me balls.
"It's always nice when you're hitting them out of the middle and you can go back to what's worked for you in the past."
Katie Mack offered support with 40 in a 66-run opening stand with Mooney, but the Queenslander then took over the innings with no other Scorcher passing 20.
Needing to pull off the highest successful finals chase in WBBL history, the Sixers looked in the contest with Sophia Dunkley and Ellyse Perry firing early.
But when Perry hit King straight to mid wicket on 29, the game swung.
Kerr (42) and Gardner (26) offered the hosts hope, but King again ensured that would be a false dawn by removing both Gardner and then Maitlan Brown in her next over.
The result means the Sixers' title drought will extend to eight seasons, after the star-studded club played in the first four WBBL finals.
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