Mooney struck eight boundaries and faced 60 deliveries while Australian teammate Jess Jonassen (37no) also ensured the asking rate never spiralled out of control.
Despite Mooney’s match-winning knock, South African import du Preez produced the innings of the contest by blasting a career-best 88 from 51 balls.
Du Preez eclipsed her previous best of 70, made against the Adelaide Strikers on Sunday, to claim player of the match honours.
After being sent in to bat, the Stars started poorly, losing openers Lizelle Lee and Elyse Villani inside the first three overs before du Preez revived the innings with a stunning counterattack.
She slammed a dozen boundaries, two sixes and combined with teenage allrounder Annabel Sutherland (37) to add 102 for the third wicket before the pair both succumbed to seamer Delissa Kimmince (3-27).
In Launceston, superstar allrounder Ellyse Perry crunched an unbeaten 70, smashing the windscreen of an ambulance with one of four sixes, as the Sydney Sixers leapfrogged to second spot on the WBBL ladder.
Perry took her season tally to 351 runs at an eye-popping average of 117, as the Sixers beat the Hobart Hurricanes by 39 runs at Invermay Park.
The captain’s knock off 56 balls propelled the Sixers to an imposing 2-172 from their 20 overs before they skittled the Hurricanes for 133 in 18 overs.
Perry was well supported by opening partner and fellow Australian international Alyssa Healy (39), who got the Sixers off to a flyer.
Ash Gardner (28) and Burns (26no) also ensured the momentum never slipped.
The Hurricanes lost three wickets in the first four overs of their response and never threatened to recover.
Captain Corinne Hall (31) and Fran Wilson (29) did their best to resurrect Hobart’s cause with a 63-run fourth-wicket stand while South African Chloe Tryon (19) was typically aggressive.
But the hosts’ lower order crumbled, with the last five wickets falling for just 18 runs.
Erin Burns (3-5) came on and mopped up the tail after Marizanne Kapp (2-18) had caused havoc with the new ball for the Sixers.
The Hurricanes have gone seven games without a victory after starting the season with successive wins while the Sixers, who started the day in sixth spot, now only trail leaders Adelaide on percentage.