Nathan McAndrew (5-16) recorded T20 career-best figures, and the best by a Thunder player in BBL history, to put last year's wooden spooners only one win away from a shot at a second title.
On a tough ENGIE Stadium pitch, the Stars attempted to chase down the Thunder's 7-135 but were all out for 114 in the 18th over of a match condensed to 19 by lightning.
The Thunder will take on the Sixers for a place in the BBL final after beating the Melbourne Stars. (Jeremy Ng/AAP PHOTOS)
Friday night's clash at the SCG will mark the first time in 14 BBL summers that the Sydney rivals have met in the finals.
Right-arm paceman McAndrew snared both Stars openers in the powerplay before dispatching Mark Steketee (18) as he provided late resistance for the resurgent visitors.
Back from the dead after a five-game win streak, the Stars' season was officially over when Doug Warren (7) slapped McAndrew to David Warner at cover with six balls remaining.
But it was spin that did the damage in the star-studded middle order.
Home and hosed!— KFC Big Bash League (@BBL) The moment the @ThunderBBL secured victory and a spot in The Challenger against the Sixers. #BBL14 pic.twitter.com/KPx1Yp7uX0January 22, 2025
Australian international leg-spinner Tanveer Sangha (2-31) swung momentum dramatically in the Thunder's favour with back-to-back wickets in the 11th over.
He most crucially caught the BBL's form player Glenn Maxwell (28) from his own bowling as the renowned spin guru skied one straight up, and then had Curran caught at extra cover by Tom Andrews.
The twin scalps came after Maxwell had looked the most comfortable of any batter on either side, notably slapping Andrews for three consecutive fours as he plotted the Stars' sixth-straight win.
Left-arm off-spinner Andrews (2-20), who was working full-time as a financial planner a month ago, trapped 20-time Test player Peter Handscomb LBW on the fifth ball he sent down.
Called in to replace Test allrounder Beau Webster, the renowned player of spin had survived an earlier caught behind chance from Wes Agar that the on-field umpire missed.
In-form Thunder batter David Warner was dismissed for a second-ball duck. (Jeremy Ng/AAP PHOTOS)
When Andrews gave Usama Mir (5) the same LBW treatment, the Stars were well into the bowlers at 7-73, but still 63 shy of their target as they limped to the finish.
Batting had also been tough going for the Thunder, who lost the toss and were sent in.
The hosts struggled to find a steady partnership after talisman Warner (0) was caught by former national teammate Marcus Stoinis at extra cover on the second legal delivery of the night.
Usama Mir was impressive taking 2-26 off his four overs for the Stars. (Jeremy Ng/AAP PHOTOS)
Matthew Gilkes (28), Sam Billings (24) and Ollie Davies (36) all made starts in the middle order but the Stars' spinners prevented any from truly thriving on the fiendish pitch.
Usama (2-26) led the charge, dismissing aggressive No.3 Gilkes when he holed out to Maxwell, with Tom Curran (2-26) dismissing Warner early on.
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