Southern Vipers all out for 231 after being put in by Lauren Winfield-Hill
Georgia Adams top scores with 80, reaching 500 Trophy runs
Northern Diamonds all out for 193 in 42,2 overs
Sterre Kalis makes 55, her third successive half century
Charlotte Taylor takes 6-34 from her 10 overs for Vipers
Southern Vipers also won every game in group stage
Kalis 38, Langston 14
Paige Scholfield is the new bowler after two expensive overs earlier on.
This one is tighter, but there is another wide - Vipers have bowled a lot of those during this game (20 in fact), but the fall of wickets has meant they have not proved costly - so far.
Kalis 37, Langston 13
Having made 80 earlier in the game, Vipers captain Georgia Adams brings herself on to bowl.
Practically no run-up and Beth Langston pushes away fine, only for the super-keen Charlie Dean to haul the ball in just short of the boundary.
Five from the over in total.
Kalis 35, Langston 10
Charlie Dean starts with a full toss and Beth Langston is down the track to drive it away for four.
Langston dabs the final delivery down to third man for two and the Diamonds need 98 from the final 20 overs.
Kalis 34, Langston 3
A good over by Lauren Bell, angling the ball into the pads of the batters from an open action. Just two leg byes and a single to Sterre Kalis conceded. Charlie Dean will continue from the other end.
Kalis 33, Langston 3
Sterre Kalis is denied four by some superb fielding on the boundary, but she completes three before swapping singles with partner Beth Langston
Langston collects another with a push to point from the final ball of the over. A productive over for the Diamonds, but they only have three wickets left.
Kalis 29, Langston 1
Charlotte Taylor is taken off with figures of 4-30 from eight overs as Southern Vipers call up seam bowler Lauren Bell.
Sterre Kalis steers down to third man but Taylor is in action in the field to keep it to two.
Kalis ends the over with a single to keep the strike - but the required rate is now up around five an over..
Smith lbw Dean 7 (Diamonds 110-7)
Linsey Smith is gifted four runs by poor fielding at point - but bowler Charlie Dean is soon smiling as her next delivery, the last of the over, traps the left-hander in front. Beth Langston is next to the crease, with 122 still needed.
Kalis 24, Smith 2
Can Charlotte Taylor take a five-for in the RHF Trophy final?
Linsey Smith flicks to backward square as the Diamonds total reaches three figures.
Sterre Kalis flashes past point for a welcome boundary - but her side need quite a few more of those if they are to win this match.
Kalis 20, Smith 1
Linsey Smith plays the ball away through the covers for a single, but the Vipers are sensing the game is theirs for the taking now.
A wide by Charlie Dean is the only other addition in that over.
Heath c Monaghan b Taylor 0 (Diamonds 96-6)
Oh dear. It's a full toss from Charlotte Taylor and Bess Heath attempts an ungainly slog sweep, which is safely pouched by Alice Monaghan at deep mid-wicket. Can Diamonds arrest this slump?
Kalis 19, Heath 0
There is a lot of pressure on 19-year-old Bess Heath. She has only reached double figures once in the RHF Trophy, but they need something special from her now.
Sterre Kalis is the key figure now for the Northern Diamonds if they are to get anywhere near this target.
Gunn lbw Taylor 9 (Diamonds 94-5)
Jenny Gunn lofts Charlotte Taylor down the ground for four, but then tries to sweep and she is gone.
That's a crucial scalp and Taylor now has 3-23 from six overs.
Kalis 18, Gunn 5
How important will that be? Sterre Kalis likes the cut and tries it again to a ball from Charlie Dean, but a thin edge goes into the gloves of keeper Carla Rudd and out again. Another 142 to win from 30 overs.
Kalis 18, Gunn 4
It's the spinners who have done the damage in this game and Charliotte Taylor twice goes past the outside edge of Sterre Kalis' bat.
Kalis tries to cut one that is slightly shorter and doesn't make clean contact, but her edge eludes the grasp of first slip Georgia Adams and runs away for four,.
Kalis 14, Gunn 4
You couldn't have anyone more experienced to come to the wicket in this situation than Jenny Gunn.
"They need to calm things, watchfully, says BBC Radio 5 live Sports Extra summariser Isabelle Westbury.
Gunn squirts the ball away for two to end the over.
MacDonald hit wicket b Taylor 0 (Diamonds 79-4)
Alex MacDonald goes back to the first ball of Charlotte Taylor's latest over, too far back.
It's the arm ball from the spinner and she hits her own stumps as she brings the bat down.
A golden duck for MacDonald - and a rare one too.
Kalis 13, MacDonald 0
Alex MacDonald is the new batter for Northern Diamonds.
They need a substantial partnership now after the loss of two wic kets in successive overs.
Campbell run out 0 (Diamonds 78-3)
Sterre Kalis plays it round the corner, Ami Campbell calls for a single but is sent back.
Lauren Bell's throw is wide of the stumps but Charlie Dean swings round to break the stumps with Campbell's bat millimetres short of her ground.
The video umpire deliberates at length, but in the end Campbell has to go.
Kalis 13, Campbell 0
Ami Campbell shoulders arms to three balls from Charlotte Taylor. It's not surprising that she wants to take a look at things with the game reaching a critical phase.
Armitage c Dean b Taylor 26 *(Diamonds 74-2)
A poor shot by Hollie Armitage brings about her downfall.
It was an unthreatening delivery by Charlotte Taylor, but she carved it carelessly straight to Charlie Dean at backward point.
Ami Campbell is the new batter.
'A poor dismissal' - Armitage falls for 26