Southern Vipers 127 for 9 (Wyatt 59, Kasperek 4-16) beat Yorkshire Diamonds 124 for 5 (Armitage 34, Rodrigues 32) by three runs
Danielle Wyatt continued her stunning Kia Super League form with a swashbuckling half-century, before Suzie Bates held her nerve in a final over thriller to hand Southern Vipers a three-run victory over Yorkshire Diamonds.
Wyatt smashed 59 from 30 balls to take her tallyto 225 runs in four days, following a supreme 110 and 56 against Surrey Stars and Western Storm.
But Bates was needed to defend seven in the final over, as Jemimah Rodrigues was bowled and Katie George and Bess Heath could only muster three runs off the 20th over.
The four-point win moves the Vipers up to second in the table and on course for a third Finals Day appearance in four seasons, and gives Diamonds an uphill battle to quality for the Hove showpiece.
Chasing 128 to win, the Diamonds lost key opener Alyssa Healy in the second over after a direct-hit run out from Wyatt.
Lauren Winfield and Hollie Armitage, who was dropped on eight, were originally stunted by the parsimonious Lauren Bell, whose four overs of in-swing only went for 13, before approaching the required rate with a 48-run stand. But both were lbw, to Suzie Bates and Fi Morris respectively, to pile the pressure on the Yorkshire middle-order, with 45 still required.
Rodrigues appeared to have taken Diamonds to the victory line with 32, but Bates used her experience to save the game.
Earlier, Wyatt continued her wonder week from ball two, after Tammy Beaumont had won the toss and batted on a hard, new surface, as she placed a six over extra cover.
The England T20 opener looked like she was playing a video game as she peppered the off-side with aggressive batting.
Two more maximums, one straight, the other over cover, were joined by seven fours, which often saw her advance at the bowlers.
Her fifty, the fourth time past the milestone in this year's KSL, came off 22 balls, as she and Bates put on 62 for the first wicket, with Wyatt scoring 49 of them.
But the end of the Powerplay signalled an incredible momentum shift toward the Diamonds thanks to some high-quality strangling - as the last 14 overs saw the Vipers only add another 65, for the loss of nine wickets.
Katie Levick, Leigh Kasperek and Katie George were the keys behind the visitors' turnaround - with the trio returning combined 12-over figures of 58 for 7.
Kasperek's figures caught the eye but it was spinner Levick, with 2 for 17, who dismissed the dangerous international pairing of Wyatt and Beaumont, in the ninth and 11th overs, the former dragging a sweep to midwicket and the later snaffled at short fine leg, which set up the procession of wickets.