Worcestershire 306 (Mitchell 75, Cox 69*, Magoffin 5-38) and 194 (Fell 85, Magoffin 5-32) beat Sussex 229 (Jordan 57*, Cummins 7-84) and 260 (Wiese 70*, Cummins 5-82) by 11 runs
Miguel Cummins bowled Worcestershire to a thrilling victory by 11 runs over Sussex at Hove after claiming 12 wickets in the match.
The Barbadian followed up his 7 for 84 in the first innings by taking 5 for 82 in the second, including the last four, just when it appeared that Sussex were heading to victory.
Chris Jordan (50) and David Wiese, who finished unbeaten on 70, put on 114 in 23 overs for the seventh wicket to get Sussex to within 45 runs of their target.
Even when Jordan was squared up by Cummins and caught behind, one ball after reaching his second half-century of the match, Wiese and Jofra Archer added 19 runs to get the target down to 26.
But Archer (16) then showed his inexperience, chasing a ball well outside off stump and edging to second slip after Cummins switched back to bowling down the slope.
Wiese cracked two boundaries as Sussex took 13 off the next over from Joe Leach to get the target down to 13 but the contest was ended by Cummins in spectacular style.
Brett D'Oliveira produced a wonderful catch at square leg to intercept Danny Briggs' leg-side flick and with the next ball Cummins sent Steve Magoffin's middle stump flying with a yorker before setting off on a celebratory run around the outfield, with his delighted team-mates in hot pursuit.
Victory has improved Worcestershire's chances of finishing behind champions Essex in the second division with a home game against Derbyshire to end their season.
They had started the final day needing nine wickets with Sussex requiring 259 runs and they made the perfect start when Leach bowled Craig Cachopa through the gate with the second ball of the day, condemning Cachopa to a pair.
Sussex were soon 42 for 4 as Cummins bowled Ben Brown with a nip-backer which kept a touch low and Leach collected his 60th wicket of the season when Fynn Hudson-Prentice (20) was bowled.
But the green shoots of a Sussex recovery began to sprout in a fifth-wicket stand of 54 between Ollie Robinson and Phil Salt, who had started to look at ease until he drove a slower ball from Charlie Morris to mid-off for 17.
Worcestershire looked to have more or less wrapped things up on the stroke of lunch when D'Oliveira plucked out Robinson's middle stump with a direct hit from backward point after confusion between him and Jordan over a single. Robinson made 42 but after lunch Jordan and Wiese took the attack back to their opponents.
Their first 50 runs came from just 41 balls and luck seemed to be running Sussex's way when Jordan's mis-timed pull off the indefatigable Cummins dropped just short of D'Oliveira at midwicket.
Jordan made 50 off 84 balls while Wiese finished from 70 off 80 deliveries with eight fours and a six, off D'Oliveira but it was Cummins, whose match figures of 12 for 166 were the best of his career, who had the final say.
"It's a shame one side had to lose and I genuinely mean that," said Steve Rhodes, Worcestershire's head coach. "It was a great game and a fantastic advert for Championship cricket.
"The wicket was strange. A lot of batsmen got out early but if you could get in and form partnerships it could be hard to take wickets. I was pleased with the way we stuck at it because when Chris Jordan and David Wiese were batting together I thought that might be it for us - it looked like being the crucial stand - but Miguel Cummins has come back and won it for us.
"To take 12 wickets and keep running in hard as he did was a mighty fine effort. He is a hard trier and it was an amazing way to finish it with those two wickets at the end."
Wiese, whose efforts had taken Sussex so close, said: "CJ (Jordan) and I decided there was no point going into our shells, we wanted to be positive because if you hung about on that wicket you would eventually get knocked over.
"We put pressure on their bowlers and we went through stages when we could score quickly. We complemented each other well and it was such a good wicket that all of a sudden it looked like we might win the game.
"But they took two really good catches and Miguel Cummins kept coming in hard at the end. It was a terrific game and it's just a shame we couldn't get over the line."