Sussex began the day on 185-6 and added a further 70 runs for their final four wickets – including captain and keeper Ben Brown who was last out for 80.
He had resumed on 64 not out but today added just one more boundary – his 12th – before giving Ed Barnard the charge and being bowled to bring an end to his 160 ball knock.
Worcestershire paceman Adam Finch had claimed his maiden first class wicket yesterday and made the first breakthrough of the day by dismissing Chris Jordan to end a partnership of 92 in 20 overs with Brown.
Jordan (52) had brought up his half century off 59 balls with a boundary off Finch but in the same over drove loosely and was caught at cover by Dell.
Ollie Robinson dominated an eighth wicket stand of 56 in 16 overs with Brown but the last three wickets tumbled for five runs.
Robinson (38) nicked Barnard through to keeper Ben Cox and Sussex debutant Aaron Thomason (4) – signed from Warwickshire - went lbw to Ross Whiteley before Brown’s dismissal.
Wayne Parnell did not add to his wicket tally today but finished with 4-92 and there were two wickets apiece for Finch (18-6-41-2) and Barnard (14.1-3-52-2).
Worcestershire began their reply half an hour before lunch and Robinson had made his presence felt with the new ball by removing the openers.
Daryl Mitchell (0) fell to a fine low catch at second slip by Laurie Evans and then Josh Dell (8) was trapped lbw in the next over.
The third wicket pair of Wessels and Ferguson led a counter-attack during the afternoon session.
Wessels completed a 56 ball half century with 10 boundaries as he and Ferguson added 93 in 25 overs.
Jordan broke the stand when Wessels (55) edged to Robinson who held onto a low sharp chance at first slip.
Ferguson went onto register his own fifty off 111 balls with seven boundaries but the game took another twist with Jordan striking twice in one over.
Ross Whiteley (21) went for an upper cut and top edged a simple catch to mid off and then Ferguson (56) drove straight to cover at 152-5.
Cox and Barnard came together and shepherded Worcestershire past the 200 mark with a partnership of 74 in 23 overs. Luke Wells ended the partnership when Barnard (29) was lbw.
But Cox, the County’s leading run-scorer in the Championship this season, continued to score freely and reached a 78 ball fifty with six fours.
By the close he had moved onto 53 and D’Oliveira 20 not out.
Following the close of play, Sussex Head Coach Jason Gillespie said: “I thought we had a good morning session. From where we were (102-6) to get over 250 and then to reduce Worcestershire to 14-2 by lunch-time was a really good effort.
“I was pretty disappointed with how we started in the afternoon and we gave two experienced players in Callum Ferguson and Riki Wessels the momentum and the impetus.
“But Chris Jordan came in after tea, got us a couple of wickets and we just had to keep chipping away.
“We spoke after tea about starting well, setting the tone and being ruthless with our line and length and make the batsmen play good shots.”