Southern Vipers 88 for 4 (Wyatt 46*) beat Lancashire Thunder 87 (Hazell 37, Smith 3-16)
Defending champions Southern Vipers bowled struggling Lancashire out for 87 in a six-wicket win at Liverpool to qualify for next week's Finals Day with a group game to spare.
The Vipers consigned the Thunder to their fourth straight defeat with an impressive, but not perfect, performance built on success with the ball.
Spin proved crucial as the Vipers took their first four wickets for just seven runs in 17 balls, although they dropped a couple of catches and later slipped to 41 for 4in reply.
The hosts, who elected to bat, failed to recover from losing key batsmen Sarah Taylor and Amy Satterthwaite in the space of five balls to the off-spin of Hayley Matthews and left-armer Lynsey Smith as the score fell to 9 for 3 in the fourth over.
Taylor was brilliantly caught one-handed for one by West Indian Matthews off her own bowling. Either side of the two international dismissals, Smith bowled Emma Lamb and Eve Jones to return 3 for 16.
Former Thunder batsman Danni Wyatt then held the Vipers chase together with a composed unbeaten 29-ball 46 following the loss of star player Suzie Bates.
New Zealander Bates still managed to stay in the thick of the action. She had Sophie Ecclestone caught at mid-on with her first ball as Lancashire fell to 57 for 8 and also took two catches.
She is the leading run-scorer in the competition with 227, the leading catcher with six and the second leading wicket-taker with seven.
Lancashire at least gained some respectability through captain Danni Hazell, who hit three sixes in 37, and Kate Cross with 19. They shared 21 for the ninth wicket to avoid the competition's lowest score across two seasons - 64.
Spin continued to prosper in the Vipers chase as left-arm spinner Ecclestone struck twice in her first over, the second of the innings, as the score fell to 7 for 2.
She had Matthews caught at mid-off and bowled Georgia Adams before Jess Jonassen had Bates caught at mid-off and Hazell bowled Mignon du Preez.
From there, Wyatt was helped along by fifth-wicket partner Arran Brindle, who hit 19 not out. They shared an unbroken 47 and won with 5.1 overs remaining.
Vipers host Yorkshire Diamonds at Arundel in their final group game on Saturday afternoon, and a win could still hand them a direct passage into the final with them three points behind Surrey. Lancashire travel to Bristol to face Western Storm.