Georgia Adams smashed the highest score of the Rachael Heyhoe Flint Trophy to send her Southern Vipers side to the final with a 32-run victory over Western Storm.
Vipers skipper Adams followed up her 89 against Sunrisers by notching an imperious unbeaten 154, the seventh highest top-tier List A score in English domestic cricket, while struggling with cramp in her calf for the last third of her innings.
Adams, who is the tournament's leading scorer with 379 runs, was brilliantly partnered by teenager Ella McCaughan (63) and Maia Bouchier (50 not out) in century stands as Vipers crashed 288-1.
And after Charlie Dean's 3-50 and Charlotte Taylor's 4-41, Vipers maintained their 100 per cent record to set up a date at Edgbaston on September 27 with a game to spare.
Captain Eve Jones hit a composed 77 to lead a successful Central Sparks chase of 218 as they inflicted a first defeat in five games upon North Group leaders Northern Diamonds at Emerald Headingley.
The six-wicket victory, secured with 3.2 overs to spare, keeps the race for a final spot at Edgbaston (September 27) alive going into next weekend's last round of matches. A third win in five games for the Sparks cuts the gap from nine points to five at the top.
That means to have any chance of qualifying for the final, the Sparks need to beat Lightning at Grace Road on Saturday with a bonus point and hope the Diamonds lose against North West Thunder at Headingley. Then it would come down to net run-rate.
Opener Jones shared a stand of 123 inside 26 overs with second-wicket partner Marie Kelly, who made 49. Even so the match was in the balance with the score at 172-4 in the 40th over.
But Poppy Davies (31 not out) and Chloe Hill (23no) calmed nerves with an unbroken 46 to ensure that Sterre Kalis' 87, which underpinned Diamonds' 217 all out, was in vain.
All-rounder Alice Capsey struck an unbeaten 73 as South East Stars strolled to a six-wicket victory against winless Sunrisers at Chelmsford.
Capsey's bustling knock took her just 75 deliveries and included nine fours as she and Aylish Cranstone (46) put together a match-winning partnership of 114 to secure the Stars' second success of the tournament.
Stars skipper Tash Farrant (3-24) made early inroads and the home side, who opted to bat, were bowled out for 198 despite a solid partnership of 55 from 57 balls between Cordelia Griffith (27) and Naomi Dattani (33) as spin duo Dani Gregory (2-30) and Capsey (0-35) stifled them through the middle overs.
Debutant Chloe Brewer (40) impressed in the chase alongside Capsey, who reached 50 off 52 balls, before Stars got home with plenty of wickets in the bank.
Skipper Alex Hartley took 4-8 to help Thunder to their second victory courtesy of a 72-run win over Lightning at Aigburth.
Thunder vs Lightning scorecard
The visitors were making good progress after Thunder posted 188-9 off their 45 overs only to collapse to 116 all out off 39.1 overs, with top-scorer Abi Freeborn (28) the last to go.
Earlier, Thunder posted a clearly competitive total in their 45 overs thanks to a half-century from Natalie Brown (52) and useful contributions from both Georgie Boyce (31) and Rebecca Duckworth (27).
The total was also boosted by the addition of 37 runs from wide deliveries, although several members of the Lightning attack bowled good spells, notably Kathryn Bryce, who took 4-38.