Sydney Thunder 6 for 143 (Haynes 48*) beat Brisbane Heat 131 (L Kimmince 37, Darlington 3-19) by 12 runs

Sydney Thunder came back from the brink to book their first WBBL final since the opening season as defending champions Brisbane Heat suffered a dramatic collapse. Hannah Darlington, who claimed last year's young player award, struck in consecutive balls in the 18th over after Laura Kimmince was removed having been close to taking the Heat across the line again.

The winning moment came when former Heat star Sammy-Jo Johnson grabbed a low caught and bowled to spark wild celebrations. The Heat's overall collapse was 6 for 12 as a campaign which had started slowly before coming to life with seven consecutive wins came crashing down.

Captain Rachael Haynes had hauled the Thunder up to a competitive total amid a stuttering innings in which Amelia Kerr and Nadine de Klerk stood out with the ball: their combined figures were 7-0-30-3. They took wickets regularly enough to stay in the contest, but Kimmince's latest onslaught appeared to have decided the game before the astonishing turnaround.

Even powerplay

Tammy Beaumont played one of her better innings of what has been a tournament where she has largely struggled, getting off the mark with a deft scoop and adding five more crisp boundaries inside the powerplay. She fell attempting another scoop, moving so early into the shot that Nicola Hancock had barely started her delivery stride, sending a simple catch looping to short fine leg. That wicket evened up the powerplay ahead of the Heat's spinners getting to work.

Kerr's deception

Like the Heat as a whole, Kerr took time to get into her stride but played a central role in the team's success. It is so rare to see her taken to by an opposition and today was no different. Her first two overs went for eight and when she returned for her third, in the 14th over, there was a brief but enjoyable contest with Phoebe Litchfield. The left hander started with perfect straight drive, but off the last ball of the over was defeated by the googly and comfortably stumped. It was the second time Kerr had claimed her this way following the group-stage dismissal at Blacktown. Either side of that dismissals were moments that stunted the Thunder just as they were building. Heather Knight drove a firm catch to cover, having not quite found top gear, and then a superbly-judged catch on the deep midwicket rope by Georgia Prestwidge removed Johnson who had threatened to open her shoulders against former team-mates.

The first wobble

The Thunder's eventual total looked short but gave them something to bowl at. In her opening over, Sam Bates, who has been one of the best bowlers of the tournament, removed Grace Harris and then Johnson struck with her first delivery when Georgia Redmayne, after a brisk 25, picked out mid-off to keep the Heat in the contest. It has been a hallmark of the Heat's campaign that there have been contributions throughout the order and the trend continued as de Klerk and captain Jess Jonassen added 46. However, just when things were under control they fell in consecutive overs: Jonassen skied a top edge to Darlington and de Klerk was run out by Beaumont's pinpoint throw. The scene was set.

The collapse

Laura Kimmince has hit the form of her life in the last couple of weeks. Before today she had rattled up 123 runs off 49 deliveries in her last four innings, taking her strike-rate to the highest in WBBL history, and struck the ball with huge power again. She had a massive stroke of fortune first delivery when the ball rolled back into leg stump but did not dislodge the bail then the next ball was launched for six. An over from Lauren Smith cost 20, swinging the game almost fully towards the Thunder who needed 26 off 30 balls. However, Georgia Voll was run out after a mix up over a second and Kerr went the same way two balls later as panic set in. Another six from Kimmince brought it back under a run-a-ball, but then she was bowled by Bates attempting a reverse sweep that wasn't really required. It became too much for the lower order as Darlington delivered her yorkers on demand and finally Delissa Kimmince hammered the ball back at her former team-mate. The Melbourne Stars await on Saturday.

Andrew McGlashan is a deputy editor at ESPNcricinfo