The hosts, set only 133 to win, romped home by seven wickets with 21.1 overs in hand. Prior hit 13 fours and a six in passing 50 for the seventh time in the competition this season.
The wicketkeeper-batsman, who presented Paul Hoffman with a difficult caught-and-bowled chance on 28, reached his 50 in fine style by hoisting Craig Wright high over mid-wicket. Prior shared an opening stand of 99 runs in 13 overs with Richard Montgomerie, but he attempted to turn a delivery from Hoffman and was caught at fine leg.
The captain Chris Adams (20) fell with his side needing only 10, chipping the pace bowler Sean Weeraratna to cover, and four runs later Murray Goodwin (4) was taken at square leg off the same bowler.
Montgomerie steered Sussex towards victory with an unbeaten 35 from 45 balls and Mike Yardy struck the winning run by pushing Ross Lyons for a single.
Sussex can now virtually secure promotion with an 11th win at the expense of Surrey Lions under the Hove floodlights tomorrow.
The Pakistan pace bowler Rana Naved took a competition-best 5 for 30 in nine overs to restrict the Scots, whose modest innings was built around a steady 51 by the skipper Jon Beukes. He shared a fourth-wicket stand of 66 in 15 overs with Cedric English (19).
Beukes faced 104 balls and his most aggressive shot came when he lifted the leg-spinner Mushtaq Ahmed high over mid-wicket for six.
The Scots lost their last four wickets for only four runs in eight balls.
Naved ended Beukes' patient knock with his penultimate delivery by bowling the South African, and last man Lyons fell to James Kirtley for a duck with two deliveries remaining.
Naved earlier struck with only his fifth ball by having Fraser Watts caught behind and Saltires' uncomfortable start continued when Ryan Watson attempted to hook the same bowler, falling to a juggling catch by Luke Wright running round from mid-wicket.Reuse content