Surrey Stars 127 for 8 (Kapp 42, Lee 40) beat Southern Vipers 100 for 7 (Bates 50*, Sciver 3-28) by four runs (DLS method)
Reigning champions Southern Vipers lost their first game in this season's Kia Women's Super League despite another impressive innings by Suzie Bates.
Bates has yet to be dismissed in the tournament after making an unbeaten 50 to add to earlier scores of 47 and 119.
But Vipers' pursuit of a target of 128 against Surrey Stars at the Ageas Bowl stalled when they lost four wickets for one run having reached 78 for 3 in the 13th over.
Rain forced the players off after 16.2 overs with Vipers 100 for 7 as Stars won by four runs under Duckworth-Lewis to claim their third straight win and virtually seal their place in finals day at Hove on September 1.
Bates and West Indies' Hayley Matthews had launched the chase with a stand of 35 before Vipers lost three wickets in nine balls, two of them to England off-spinner Laura Marsh.
Bates and Arran Brindle then put on 37 for the fourth wicket and looked to be steering the hosts to victory before the dramatic collapse.
Brindle was leg before to Nat Sciver who then ran out Georgia Adams from midwicket in the next over. In her next over, Sciver bowled Vipers' captain Charlotte Edwards round her legs and trapped Carla Rudd lbw two balls later.
Vipers took 16 runs off the 16th over with Bates moving to her half-century with successive fours as they tried in vain to get ahead of Duckworth-Lewis before the rain got too heavy.
Earlier, Stars were indebted to their two South Africans, Lizelle Lee and Marizanne Kapp, to get them to 127 for 8 after winning the toss with 56 runs coming in the Powerplay.
Lee, making her first appearance in the competition, crashed 40 off 24 balls with eight fours as she dominated to the extent that no other batsman scored a run until the fifth over. She looked in prime form until mis-timing a drive to extra cover in the seventh over.
Kapp held the rest of the innings together with 42 from 48 balls but some accurate bowling restricted Stars to 50 runs between the 6th and 16th overs, during which time they lost three wickets including Sciver, who was run out by Matthews' direct hit from mid-off.