Former national captain Alex Blackwell helped Sydney Thunder steal an unlikely four-wicket win over the winless Melbourne Stars in the WBBL.

Set 142 for victory, the Thunder looked in trouble at Bankstown when they slumped to 5-88 and needed 51 off the last five overs.

But with Blackwell at the crease, the home side had a pulse and the veteran timed the chase to perfection, digging in early and launching late to remain undefeated on 45, steering the Thunder home with two balls remaining.

Opener Rachel Priest (45) started the pursuit aggressively but when she was trapped in front by teenaged spinner Madeline Penna, who bowled brilliantly to snare 4-20, the Thunder stalled.