Southern Vipers 208 for 7 (Adams 51, Elwiss 43, Norris 3-45) beat Thunder 206 for 9 (Smale 99, Mack 37, Smith 3-19) by three wickets
Nancy Harman got Southern Vipers over the line in a tight three-wicket victory over Thunder to give the holders three wins in a row.
Allrounder Harman, in her first appearance of the season, came to the crease with Vipers wobbling on 136 for 6 needing 207 - and behind the DLS with rain about. But she beat her previous best of 23 not out to guide her side to victory, and continue Vipers' unbeaten record against Thunder.
Earlier, England A batter Seren Smale beat her previous best of 94 - scored against Central Sparks last season - and bagged her third career Rachael Heyhoe Flint Trophy fifty but ended up heartbroken after being run out on 99.
Vipers chose to bowl first and strangled Thunder in the opening 10-over Powerplay, with Shachi Pai bowled by Linsey Smith and only 16 runs coming.
But Smale and Katie Mack got the innings into gear with a risk-free approach of singles and only eight boundaries making up their 94-run stand. The partnership underpinned the innings, albeit not coming at any great speed, as Smale reached her half-century in 84 balls.
She earned lives on 53 and 65 - a caught and bowled spilled by Smith and a drop at deep midwicket - but showed great skill to pepper her innings with six fours, all coming in the V.
Mack and Fi Morris both fell with the score on 111 within two balls of each other. The Australian was involved in a classic run-out mix-up before Morris skied a pull to give Alice Monaghan the Vipers' first wicket to pace this season.
Ellie Threlkeld was bowled trying to ramp Mary Taylor and Naomi Dattani drove straight back at Charli Knott, but Danni Collins joined with Smale to put some impetus into the back end of the innings.
All eyes were on whether Smale could convert to three figures for the first time in her career. She had to contend with not getting a great deal of strike and wickets falling at the other end.
Collins - after putting on 41 in a 21-ball 23 - and Tara Norris fell to Smith in consecutive balls. The left-arm spinner ended up with 3 for 19, and the most economical spell for a Vipers bowler for the second week in a row.
Phoebe Graham was castled by Taylor as Smale needed five runs in the final two overs. But she only faced four balls before she was run out attempting to reach the landmark and she remained sprawled in her dived state for a while before dragging herself off.
Vipers' reply got off to a stuttering start as Norris hooped an in-swinger to bowl Ella McCaughan with the fifth ball of the innings before Knott ended her run of 41, 58 not out and 40 when she hit to short midwicket.
With rain around, Vipers tried to match the DLS target - Georgia Adams crashing a series of straight boundaries with aplomb. But Abi Norgrove advancing and getting castled to make it 46 for 3, saw DLS rocket from 52 to 70.
Adams and Georgia Elwiss put Vipers comfortably ahead of the rate with a partnership oozing in quality before Elwiss was strangled down the leg-side and Emily Windsor was beaten for pace by Graham.
Adams reached her 50 in 62 balls - her 15th half-century - but top-edged Dattani behind to swing things back to the visitors. Then Rhianna Southby, Harman and Monaghan scored the last 72 runs to guide Vipers to victory with 39 balls to spare.
