Worcestershire struck back with five wickets during the afternoon session after being on the receiving end of a 70 ball century from Sussex's Matt Machan on day one of the LV = County Championship clash at Hove.
Machan, who played in all six of Scotland's World Cup matches, helped Sussex race to 153-1 off 31 overs by lunch – with the aid of a short boundary – after skipper Ed Joyce had elected to bat.
There were two wickets apiece for Charlie Morris and Jack Shantry and one for Gareth Andrew and Alex Gidman as Sussex reached 300-6 off 64 overs by tea.
Morris made an early breakthrough in dismissing Luke Wells who, playing away from his body, was caught in the gulley by Tom Kohler-Cadmore when on nine and the total 16-1 in the sixth over.
Wells failed to add to his score after being dropped in the previous over from Andrew by Tom Fell at third slip.
Joyce survived one confident lbw shout from Andrew who then conceded three fours in an over to Machan on a good pitch.
Machan finished the session on 87 not out from 63 balls with 12 fours and three sixes in an unbroken second wicket stand of 137 with Joyce who was unbeaten on 44.
Shantry struck in the third over after lunch. Joyce on 49 flashed at a delivery from Shantry and Gidman at first slip held onto a sharp chance with the score 161-2 in the 34th over.
Joyce and Machan added 145 in 27.4 overs for the second wicket.
Machan went to his century off 70 balls with his fourth six – off Shantry – and he also hit 13 boundaries.
Morris picked up his second wicket when Craig Cachopa, a team-mate of Worcestershire's NatWest T20 Blast player Colin Munro at Auckland, was undone by a delivery of extra lift after making eight.
It hit the shoulder of the bat and Worcestershire skipper Daryl Mitchell held onto a fine diving catch at second slip as his side secured their first bowling point.
Machan's fine knock ended after making a career best 135 when he holed out to Richard Oliver in the deep off Shantry with the total 231-4.
He struck four sixes and 18 fours and faced just 99 balls.
Andrew collected his first wicket when Ben Brown (19) went for the hook and top-edged a catch to substitute Joe Leach.
Luke Wright scored freely and reached his third half century of the season from 57 balls with eight fours out of 284-5.
But Gidman ended his knock on 51 in his second over when Wright looked to pull square of the wicket and top edged a catch to Sachithra Senanayake in front of the pavilion.