Luke Wells led a Sussex recovery after Worcestershire had made early inroads with the ball on the opening day of the Specsavers County Championship match at New Road.
The visitors elected to bat and were reduced to 7-2 with Worcestershire skipper Joe Leach and paceman Josh Tongue a threat with the new ball.
Sussex debutant Angus Robson failed to trouble the scores before he edged the third ball of the day from Leach and keeper Ben Cox pulled off a superb catch diving in front of first slip.
It was Leach’s 45th Championship wicket of the campaign.
Then Harry Finch also departed for a duck as he nicked Tongue through to the Worcestershire keeper.
It became 49-3 as Stiaan van Zyl (24) slashed at Ed Barnard’s second delivery and George Rhodes at second slip clung onto the sharp chance.
But Wells, who had scored a century in the match between the counties at Hove, brought up his half century out of 96-3 in the 28th over. It came off 87 balls and contained seven fours.
He survived one chance on 32 to Daryl Mitchell low at second slip during a testing spell from John Hastings.
By lunch the left hander had moved onto 58 and Chris Nash 19 out of 106-3 off 29 overs in a stand so far worth 57.