Vipers looked for all the world like they’d come up short in their pursuit of 184 when Katie Levick (1-20) and Jenny Gunn (3-31) reduced them to 109-7.
However, Portsmouth-born Windsor (47 not out) and Norris (40 not out), who had earlier returned two for 36 trumped the Diamonds with an unbeaten stand of 78 as the reigning champions sneaked home by three wickets with two balls to spare.
All this came after Ami Campbell (60) scored a half-century for the second time in four days to drag Diamonds from 116-8 to 183 all out, Georgia Adams taking 4-35. It meant more heartbreak for Diamonds who lost to Vipers in last year’s final and who were bridesmaids at the Charlotte Edwards Cup showpiece earlier this month.
Diamonds sent Linsey Smith in to open, but hopes she’d pinch-hit proved unfounded, though Hollie Armitage was first to go after being bowled by Paige Scholfield. Smith limped to 31 from 65 balls before becoming the first of Adams’s victims, sparking a collapse where three wickets fell for a single.
Bess Heath struck the first boundary for 11 overs before Tara Norris trapped her lbw, replays suggesting the ball pitched outside leg stump. Another collapse followed, four wickets tumbling for four runs and at 116-8 Diamonds were in dire straits.
Campbell though refused to go quietly, striking four boundaries to reach 50 in 63 balls and by the time she holed out in the final over the last two wickets had mustered 67.
Their total of 183 looked worth more when Beth Langston plucked out the off stumps of Adams and Ella McCaughan, both for nought, to leave Vipers 6-2.
Maia Bouchier, released from the England squad to play in the final, struck the game’s first six – an effortless pull over square leg - but Phoebe Graham removed Georgia Elwiss as she was caught behind. Bouchier forged on, taking two fours from one Graham over only to be stumped by Heath off the spin of Levick, who in company with Smith slowed the run chase to a crawl.
With the pressure mounting, Jenny Gunn castled Gabi Lewis, before having Scholfield stunningly caught by Armitage and trapping Carla Rudd first ball.
But Norris saved the hat-trick and so began the match-winning stand.
Northern Diamonds bowler Jenny Gunn said: “I don’t really think it should have got that close with just two balls left and that just shows how well we bowled, but also it’s annoying they had a 78-run partnership at the end.
“I guess it was the same with our innings really where just having our partnerships at the end got us to a total we hoped to defend, but it wasn’t meant to be and it just shows the depth of women’s cricket at the moment.
“Ami can bat and fair credit to Katy Levick and Rachel Slater for staying with her and getting a score on the board because at one stage we weren’t going to be competitive enough.
“It’s frustrating to not win a final but what can you do. That’s cricket and why we play sport. It’s not as if we didn’t give it everything, I’m proud of all the girls.”
Southern Vipers’ seamer Tara Norris who took 2-36 and scored 40 not out in the match-winning stand said: “I thought we bowled really well at the start and we knew it was an achievable total to chase down. I was glad I was there at the end with Winny (Emily Windsor) to see it home.
“When I walked out I just said to Winny we’ve got to take it deep. If we bat the 50 overs we win the game. So it was about holding our nerve just that little bit longer, playing our usual cricket, nothing high risk.
“I guess it was just pure desire. We spoke to Lotte (Charlotte Edwards) today and there was that hunger to win. This was my third final and I’ve never won anything so I didn’t want to walk off the pitch until the game was over.
“I knew I had it in me and knew I wanted to do well for the team. I personally don’t feel I’ve contributed enough in the 50-over comp, so today I saw a real opportunity to go out there and contribute to my team and do them proud.
“I was devastated not to have got over the line in the Charlotte Edwards Cup and I think that was in the back of my mind. I knew I didn’t want to feel that way again.”