Thunder beat Northern Diamonds by seven wickets to reach Finals Day in the Charlotte Edwards Cup where they will play defending champions Southern Vipers in the semi-final.
Diamonds’ innings never got going as they were bowled out for 96 with eight balls of their 20 overs remaining.
Needing to reach their target within 16 overs to leapfrog Diamonds into the top three, Thunder raced to 97-3 off 15 to seal their semi-final place, let by Fi Morris’ unbeaten 42.
Southern Vipers comfortably beat winless Sunrisers to finish second in the group.
Batting first Sunrisers were indebted to Cordelia Griffith’s 65 as they posted 114-7, but Vipers cruised home thanks to Georgia Adams’ unbeaten 63, winning by five wickets with 5.1 overs to spare.
The winner of Saturday’s semi-final at New Road will play The Blaze in the final afterwards.
In the two other games, fifth-placed Western Storm’s outside chance of a top-three finish ended with defeat by seven wickets to unbeaten group winners The Blaze by in Cardiff.
And in Canterbury, South East Stars held off Central Sparks’ challenge to win by six runs with neither side able to qualify for the knock-out phase.
Fragile batting costs Diamonds dear
Diamonds came into the final group match four points clear of Thunder in the last qualification place in the table and just needing to avoid any carelessness to be certain of making the semi-final.
But cracks soon appeared as three wickets were lost in seven balls for four runs – including captain, and second-leading run scorer in the competition, Hollie Armitage for a duck – leaving them 15-3 in the third over.
They lost wickets regularly against Thunder’s disciplined attack and with seven down, three more quickly followed – again in seven balls for four runs – as Scotland off-spinner Olivia Bell finished with a career-best 3-9.
Inspired by their performance in the field, Thunder’s batters attacked their 16-over target with gusto as they cracked 28 off their first three overs.
They never surrendered the momentum with Morris spearheading the run chase with a classy unbeaten knock off 34 balls to ensure Thunder picked up four points for the win and the crucial bonus point that lifted them above a dejected Diamonds, who slipped out of the top three following a third straight defeat.