Sussex 220 and 312 for 6 (Alsop 137*, Carter 55) drew with Worcestershire 438 for 5 (Libby 215)
Worcestershire picked up 14 points but they are 28 points behind second-placed Middlesex with two games to play and will almost certainly be in the second division again next season. Sussex remain seventh and have little prospect of improving on that position with two matches to go.
The visitors were ultimately left to rue the loss of 84 overs to the weather. There were a couple of moments on the final day when they sensed an opportunity but Alsop held things together impressively for the hosts.
The wicket at Hove didn’t really deteriorate but Sussex were still 130 runs in arrears when they lost opener Orr, leg before when Ben Gibbon found some late inswing.
Alsop had come to the crease in the sixth over of the day after nightwatchman Brad Currie had two stumps knocked over by Josh Tongue’s inswinger.
It was hard work at first but gradually Alsop, fluent as always on the leg side, and Clark began to find some rhythm as the ball softened.
Clark went down the wicket to hoist Brett D’Oliveira for a straight six but in the next over he was brilliantly caught down the leg side by the diving Gareth Roderick off the persevering Dillon Pennington after adding 83 in 27 overs with Alsop.
Worcestershire sensed their chance but Carter proved an excellent foil for Alsop in a fifth wicket stand of 110 in 30 overs.
Alsop went to his century with a clip to the mid-wicket boundary off Tongue but two wickets in five balls after tea, when they took the new ball, gave Worcestershire renewed hope.
Carter, who hit nine fours as he passed fifty for the sixth time this season, was beaten by a fine delivery from Pennington which trimmed the bails.
Then in the next over Joe Leach bowled Fynn Hudson-Prentice with one which kept low. Sussex’s lead was just 64 at that stage and their lengthy tail was exposed.
But Alsop stood firm and James Coles belied his inexperience to offer solid support at the other end as they put on 30 runs before the players shook hands. Alsop’s innings spanned 228 balls and contained 18 fours and he departed to a standing ovation.