Southern Vipers 138 for 6 (du Preez 50, Matthews 40, Levick 3-21) beat Yorkshire Diamonds 108 (Brunt 42) by 30 runs
Reigning champions Southern Vipers are through to the final of this year's competition after an unexpected end to the group stages of the Kia Super League.
Vipers did their bit by ending Yorkshire Diamonds' hopes of joining them at Finals Day when they won by 30 runs at Arundel.
Meanwhile, Surrey Stars' unexpected defeat to Loughborough Lightning meant Vipers overtook Surrey to finish top of the group. They will play the winners of Surrey's clash with Western Storm at Finals Day at Hove next Friday.
Vipers made 138 for 6 after they were put in on a slow pitch. Diamonds began their reply promisingly but from 31 for 0 in the third over they collapsed horribly, losing five wickets for just four runs in 18 balls. Katherine Brunt top scored with 42 but they were bowled out for 108 in the 19th over.
For once Vipers' batting fired without the prolific Suzie Bates. The New Zealander was brilliantly caught at long on for 12 in the fourth over by Sune Luus but her fellow overseas players made up for her rare failure.
Opening partner Hayley Matthews scored 40 off 38 balls with three fours and two sixes, both struck cleanly down the ground, before Mignon du Preez went to her first half-century in the tournament from 35 just deliveries. The South African hit six fours as Vipers accelerated towards the end, scoring 37 in the final four overs.
Katie Levick picked up two wickets in the last over to finish with 3 for 21 but a target of 139 on a slow pitch was always going to test Yorkshire, even though Linsey Smith's absence, after she suffered an asthma attack before the start, left them a specialist bowler short.
They began well with Sri Lankan Chamari Atapattu hitting two fours and two sixes in the first four overs. But when Lauren Winfield was smartly stumped by Carla Rudd off Arran Brindle the innings went into steep decline. Luus was run out two balls later then Bates claimed the key wicket of Atapattu (21), who was leg before swinging across the line. Sophie Devine fell in similar fashion and Yorkshire were 35 for 5 when Jenny Gunn was bowled round her legs by Tara Norris.
Brunt hit eight fours to keep Diamonds in with a chance but when she was run out backing up too far by Bates' deflection onto the stumps in the 17th over Yorkshire's race was run.