Chasing 150 on Thursday at Junction Oval, the Scorchers were cruising at 2-116 in the 13th over.
After taking two wickets, Sophie Devine had been promoted to open and her blazing innings had put Perth in what appeared to an impregnable position.
But first Georgia Wareham bowled Maddy Darke for 15 and two balls later, Alice Capsey had opener Beth Mooney stumped for 41.
The English spinner stunningly snared another two wickets in the same over to leave the Scorchers in major strife at 6-118.
But Freya Kemp (18 not out) and Lilly Mills (15no) stopped the rot, guiding Perth to 6-151 with eight balls left.
Capsey snared 4-14 from her three excellent overs of off-spin.
Earlier, Devine had taken the key wicket of Renegades No.3 Sophie Molineux for only five before Melbourne were all out on the last ball of their 20 overs.
The New Zealand star then moved up the order and belted the Renegades attack around Junction Oval, hitting six fours and two sixes in her knock of 46 from just 24 balls that ultimately proved the difference.
The Renegades would have joined Hobart at the top of the ladder with a win. Instead, they stayed third ahead of Saturday's big local derby against the second-placed Stars.
Chloe Ainsworth claimed two wickets in the 13th over of the Renegades' innings and they were struggling at 7-94.
Nicola Faltum and Sarah Coyte then had a quickfire stand of 46 for the eighth wicket that meant the home side posted a competitive score.
Coyte was run out for 24 from 18 balls and Fulton top-scored with an unbeaten 41 off 28 deliveries, with six fours.
Ainsworth returned a miserly 2-17 from her four overs and Amy Edgar also claimed two wickets.
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