Surrey Stars 169 for 6 (Lee 72, Kapp 48, Nicholas 3-20) beat Western Storm 117 (Sciver 3-11, Hartley 3-28) by 52 runs
A blistering innings of 72 from 44 balls from South African opener Lizelle Lee set up Surrey Stars' fourth win in four games of the 2017 Kia Super League, and secured their place in Finals Day at Hove on September 1.
Lee hit seven fours and six huge sixes against Western Storm, which helped guide Surrey to a formidable total of 169 for 6 from their 20 overs in front of a crowd of around 1,000 at the Kia Oval.
Stars did not have things all their own way early on, however, as they lost the toss and were invited to bat, then saw England international Tammy Beaumont dismissed by the first ball of the innings. She was lbw to Claire Nicholas' spin.
That did not perturb Lee, who proceeded to put on 103 for the second wicket with fellow South African Marizanne Kapp. Lee lap-swept and cut powerfully before being dropped on 31 at midwicket off the bowling of Stafanie Taylor, who she then swept for two sixes.
Lee also got after England and Storm captain Heather Knight, hitting her for three sixes in an over before cutting straight to cover-point. That brought captain Nat Sciver to the crease, and she hit six fours in a hard-hitting cameo of 30 from 18 balls before being caught at long-on off Nicholas.
There were a flurry of wickets at the end of Surrey's innings, with Nicholas also dismissing Kapp for 48 to finish with 3 for 20.
In the face of such a formidable total last year's finalists never really got going, with Kapp trapping England pair Knight and Fran Wilson with consecutive balls in her second over. Rachel Priest looked dangerous before she, like Taylor, fell to Sciver, who is the tournament's leading wicket taker with 10.
With their high-class top four gone, the job was left to Storm's youngsters. Sophie Luff was caught at cover off Alex Hartley, but some resourceful hitting from Georgia Hennessey and Alice Macleod saw them share 59.
But they fell in consecutive overs to the spin of Laura Marsh and Hartley, bringing about a collapse of four wickets for six runs. Sciver returned to bowl the final over, having Holly Huddleston caught at long-on to secure at 52-run victory as Storm were bowled out for 117.