Northern Diamonds 144 for 4 (Kalis 55*) beat North West Thunder 143 (Brown 32, Langston 3-18) by six wickets
Northern Diamonds secured a convincing win over cross-Pennine rivals North West Thunder to qualify for next Sunday's Rachael Heyhoe Flint Trophy final at Edgbaston, where they will play Southern Vipers.
Former England fast bowler Beth Langston returned an excellent 3 for 18 from 8.5 overs as the Thunder, who elected to bat, were bowled out for 143 at Emerald Headingley.
The Diamonds then secured their fifth win from six to top the North Group by chasing down their target for the loss of only four wickets with 20.2 overs to spare. Netherlands international Sterre Kalis top-scored with an unbeaten 55 off 67 balls, including nine fours.
On a glorious late September day in Leeds, the Thunder were hurt by the loss of two wickets in the first 20 balls of the contest, including Langston bowling Laura Marshall, and later five wickets for 18 runs as they slipped from 91 for 3 to 109 for 8.
Langston returned in the latter stages of the innings to bowl Liberty Heap and Rebecca Duckworth, picking the ideal time to return her best figures of the competition on a true pitch. Her new ball partner, Phoebe Graham, also struck twice, as did Jenny Gunn - she also later contributed an unbeaten 26 - and Katie Levick. Upon her return from training with the England squad, left-arm spinner Linsey Smith also added a wicket.
The inexperienced Thunder, who have been encouraged by two wins from their six games, were eyeing a recovery from 31 for 3 in 10th over as opener Georgie Boyce and Nat Brown were sharing 60 for the fourth wicket. They hit 29 and 32 respectively, uniting for 11 overs.
In that period, the Diamonds looked a touch ragged and will be keen to rectify an issue with wides that reared its head for the fourth game running. In those games combined, they have conceded 95 runs in wides, including 25 in this game. If they do that against the Vipers in the final, it could be very costly.
In reply, the Diamonds, who have won both matches against the Thunder this summer, wobbled only briefly as they lost two wickets in the 21st over to slip to 90 for 4 before Kalis steered them home.
Rachel Hopkins was bowled around her legs in the seventh over by left-arm spinner Hannah Jones, but captain Hollie Armitage hit six boundaries in a 50-ball 36 to help take the target below 100. Armitage offered a sharp return catch to Thunder skipper Alex Hartley in the 16th over.
In the 21st, off-spinner Heap then had Ami Campbell stumped before Alex MacDonald was run out following a mix-up with Kalis three balls later to make it 90 for 4.
But 21-year-old Kalis, who hit 87 in last Sunday's defeat against Central Sparks, found an ally in former England Ashes and World Cup winner Gunn.
Gunn was the aggressor with five fours in 35 balls as the pair shared 54 inside nine overs, while Kalis - strong on the sweep - reached 50 off 64 balls in a bonus-point win.