Brisbane Heat 160 for 8 (Heath 29, Johnson 3-39) beat Sydney Thunder 138 for 9 (Athapaththu 39, Jonassen 4-26) by 22 runs

A star turn from spinner Jess Jonassen lifted Brisbane Heat to a 22-run win over Sydney Thunder and into the Women's Big Bash League (WBBL) finals.

Chasing 160 for 8, Thunder fell short with Jonassen snaring four wickets in Friday's fixture at Adelaide Oval. Heat's victory in their last regular-season game ensured they reached the finals - they were in third spot on 16 points.

Thunder are fourth on 15 points with one game remaining, two points clear of fifth-placed Hobart Hurricanes who also have one match left before the finals.

But Hurricanes would need a massive win over ladder leaders Adelaide Strikers on Sunday to boost their run-rate ahead of Thunder, who meet Sydney Sixers in their last game before the playoffs.

The team that finishes top will gain direct entry into the final which they will host on December 2. The second-placed side will host the Eliminator and Challenger finals.

Jonassen was pivotal in Friday's win, taking 4 for 26 from her four overs, after Thunder openers Chamari Athapaththu and Phoebe Litchfield gave the Sydney-siders a brisk start.

But Thunder lost six wickets in an eight-over span to lose momentum as Jonassen turned the screws. She claimed the key duo of Athapaththu and Marizanne Kapp as the chase stalled.

Earlier, Heat's Bess Heath made 29 from 25 balls to top score during an even batting effort. Seven batters made more than 12 with opener Georgia Redmayne (21 from 21), Amelia Kerr (20 from 17) and Laura Harris (19 from 9) making handy contributions.

Heat's innings finished with a flourish as Georgia Voll smacked a six in her rapid-fire 18 not out from only eight balls.