Skipper Georgia Adams struck a magnificent unbeaten 154 as Southern Vipers reached the Rachael Heyhoe Flint Trophy final with a game to spare.
Adams saw her side to 288-1 against main group rivals Western Storm, who made 256 all out in reply.
Northern Diamonds remain clear favourites to win the other group, but suffered their first defeat, by six wickets to Central Sparks.
Elsewhere, there were victories for South East Stars and Thunder.
Southern Vipers have won five out of five so far and are now nine points ahead of Storm with only the final round of group matches to play, with Sunrisers the only team still to register a victory.
In the North Group, Diamonds are five points clear of Central Sparks and need only one more to be mathematically certain of their place in the final on 27 September.
Adams shows consistency
Having begun the competition by taking part in two century partnerships with England’s Danni Wyatt, Adams exceeded them both by putting on 155 with Ella McCaughan at the Ageas Bowl.
Fi Morris eventually bowled McCaughan for 63, but Adams carried her bat through the entire innings, hitting 20 fours, and Maia Bouchier made an unbeaten 50 off 47 balls as they added 133 to the end of the Vipers innings.
It was the second highest total in the Trophy, but Western Storm were still in with a chance as captain Sophie Luff (73) and Natasha Wraith (68) shared a fourth-wicket stand of 129 in 24 overs.
Luff’s runs aggregate of 336 is second only to Adams and her dismissal, caught off medium-pacer Charlotte Taylor (4-41), left her side too much to do and they were all out from the final ball of their innings.
“I’m chuffed to bits for the girls that we have managed to get there, and so soon, ” said Adams. “I would have liked a new calf at one stage. I’ve never normally be the one to cramp up. I am really glad I pulled through and was on the field for all 50 overs fielding.”
In the other South Group game at Chelmsford, Tash Farrant took 3-24 as Sunrisers were all out for 198 and South East Stars reached 199-4 with almost 13 overs to spare as Alice Capsey made 73 not out off 75 balls.
Missed opportunity for Diamonds
At Emerald Headingley, the Northern Diamonds innings was held together by Netherlands international Sterre Kalis, who had previously been dismissed for three successive ducks.
She made 87 before being caught off Liz Russell (4-28) and they were all out for 217 as Emily Arlott bowled Beth Langston (26) with the final ball of the innings.
The Sparks reply began badly as Gwenan Davies was lbw to the second delivery of Langston’s opening over.
Captain Evelyn Jones remained calm, however, and she added 123 with Marie Kelly (49) to lay the foundation for the chase.
And, although she gave a return catch to spinner Katie Levick on 77, Poppy Davies (31) and Chloe Hill (23) finished the job as they reached 218-4 in the 47th over.
“Our first priority was to win today, rather than do it with a bonus point,” said Jones. If we’d have got close, we’d have had a go. But we definitely need one one next week, and hopefully it’s enough to get us to the final.”
Thunder came out on top in the clash of the elements with Lightning at Aigburth, with Natalie Brown’s 52 helping them to 188-9 before Alex Hartley produced incredible figures of 8-40 from 10 overs as their opponents were bowled out for just 116.
“When I lost my England contract I began to undercut the ball and stopped turning it and overspin is something I’ve been working on,” said Hartley. “I’m pleased with the figures but I was searching for the five-fer at the end.”
Results and scorecards
Northern Diamonds (217) lost to Central Sparks (218-4) by six wickets – scorecard
Thunder (188-9) beat Lightning (116) by 72 runs- scorecard
Southern Vipers (288-1) beat Western Storm (256) by 32 runs – scorecard
Sunrisers (198) lost to South East Stars (199-4) by six wickets – scorecard
Saturday, 19 September
- Headingley: Northern Diamonds v Thunder
- Kia Oval: South East Stars v Southern Vipers
- Bristol: Western Storm v Sunrisers
- Leicester: Lightning v Central Sparks