After four sessions dominated by batsmen as Worcestershire made 491, the visitors came under severe pressure when set to make 342 to avoid the follow-on.
Half the side went for 116 before deputy captain Ben Brown and Matt Machan led a partial recovery, a stubborn sixth-wicket partnership of 56 helping their team to 192 for six, still 299 behind, at the close.
In a strong and relentless performance by the bowling unit, Worcestershire took five wickets in 21 overs after ending an opening stand of 58.
Ed Barnard made the breakthrough by bowling Ed Joyce for 31, a big wicket after the left hander’s career-best score of 250 in last week’s rain-hit game against Derbyshire.
When Chris Nash was leg-before in the first over of Matt Henry’s second spell, the balance of power was held by the home side’s seam quartet.
Luke Wells (16) shovelled a short ball from Joe Leach to fine leg, where Jack Shantry held a good catch, and in Leach’s next over Ross Taylor was lbw for 11.
More trouble hit Sussex soon after tea when Shantry claimed his first wicket, Tom Kohler-Cadmore taking the chance from Harry Finch (5) at first slip, but Brown and Machan picked a good time to make a significant contribution.
With a previous highest score of 22 not out, Brown advanced to 49 not out and Machan scored 36 before he was out sweeping, a first championship wicket of the season for Brett D’Oliveira after his successful conversion to opening batsman.
Worcestershire made the most of the morning session in adding 109 to the first-day score of 382 for four. When Henry was caught at point off Ollie Robinson on the stroke of lunch, the total was their highest in 156 first-class meetings with Sussex, surpassing 464 at Hove in 2010.
The key to reaching this milestone was the overnight partnership which was extended to 120 by Kohler-Cadmore (51) and Ross Whiteley, who hit a six and nine fours in a season’s best knock of 71 from 121 balls. They became the third and fourth players in the innings to reach 50 but no one posted a century.
Kohler-Cadmore became a second victim for the impressively accurate Steve Magoffin, who bowled 29 overs for 56 runs, and Stuart Whitttingham dismissed Whiteley and Leach (26) for the best return of three for 86.
The more expensive Lewis Hatchett claimed one success when Ben Cox (30) was snapped up at backward point and Barnard (14) holed out at deep square leg to give leg-spinner Wells figures of three for 105.
While Sussex stuck at their task, at that stage there was nothing to suggest that their own batsmen would struggle as they did. The first ten in Worcestershire’s order all got into double figures.
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