Southern Vipers 287 for 9 (McCaughan 83) beat Northern Diamonds 162 for 7 (Winfield-Hill 63, Dean 4-34) by 70 runs (DLS method)
Ella McCaughan blasted a half-century to take her past 1,000 Southern Vipers runs and help her side win back-to-back Rachael Heyhoe Flint Trophy matches.
Opener McCaughan was belligerent in her 97-ball 83, with Charli Knott continuing her fine start to life in the UK with 40 - as Vipers totted up 287.
Diamonds stuttered in response before Lauren Winfield-Hill's 63 and Erin Burn's 45 steadied things before another stumble - with Charlie Dean claiming 4 for 34.
Rain ended proceedings with Diamonds 70 runs short of the DLS target of 232 and put an end to Diamonds' winning start to the season.
Diamonds skipper Hollie Armitage stuck Vipers in - with weather around and the benefits of chasing with DLS - but McCaughan and Maia Bouchier began like they were up against some rain.
The duo had 50 up inside eight overs, with McCaughan the unlikely aggressor of the partnership, while playing a series of sumptuous shots - none more so than the cut, on drive and cover drive combo in the third over off Lizzie Scott.
The 21-year-old had a strike-rate of 55.77 in List A matches before this match but blasted her way to her sixth Rachael Heyhoe Flint Trophy half-century.
Bouchier had been dropped on 14 at gully, one of four drops across the Vipers innings, but fell for an entertaining 26 when she top-edged Phoebe Turner - giving the medium pacer her first.
Knott continued the fast pace with some well-judged dabs to the third boundary, as the Australian followed up her 41 and 58 not out in her opening two Viper appearances with a run-a-ball 40.
The end of her 93-run stand with McCaughan, coupled with the pair departing in back-to-back overs, began a fightback for Diamonds which stopped Vipers from reaching 300.
Emily Windsor, Freya Kemp, Charlie Dean and Georgia Adams all got starts but couldn't blow the visitors away like the top order had.
Australian Burns started finding good turn, which did for Windsor and Kemp, for her 2 for 56, while Phoebe Turner completed her back-to-back three-wicket hauls when she had Adams caught behind.
Vipers' 287 for 9 felt lower than it could have been but Linsey Smith bowling Emma Marlow in the sixth over gave them early control of the reply.
In reply, Marlow - opening in the Rachael Heyhoe Flint Trophy for the first time with Sterre Kalis on international duty - had her middle stump knocked back by Smith.
Dean had Armitage leg-before and Bess Heath stumped in quick succession as the chase struggled to get going.
Winfield-Hill and Burns got things pointing in the right direction with a punchy partnership for the fourth wicket.
Former England opener Winfield-Hill found the gaps with ease to show her quality in her second fifty of the campaign - coming in 54 - albeit having been dropped on 9.
The stand with Burns reached 82, and had almost caught up with the DLS target, before a flurry of wickets ended the Diamonds' hopes.
Burns was brilliantly caught at short third, Winfield-Hill picked out deep midwicket, Phoebe Turner was castled and Leah Dobson missed a straight one to give Dean her fourth.
Rain, which had been light for a while, started to come down heavier just after 4pm to take the players off, with the DLS target 232.