Lancashire's hopes of relying on events at Hove to earn heir first outright County Championship in 73 years could be dependent on the weather.
Relegated Worcestershire, 96 for two, need another 287 runs to save the follow-on, after Sussex scored maximum bonus points in totalling 532 in their quest to retain the title.
They need seven more points from this match than anything Lancashire, the leaders, obtain against Surrey at The Oval.
Sussex dangerman, Pakistani leg-spinner Mushtaq Ahmed, ended a dogged opening stand of 79 by Daryl Mitchell and Stephen Moore. Doughty Mitchell has reached 36 while Graeme Hick, his overnight partner, needs another 68 runs to reach 1,000 in a season for the 20th time.
Sussex, resuming on 287 for four and who have not lost a four-day match at Hove for three years, were boosted by a 120-run ninth-wicket stand in 18 overs between Robin Martin-Jenkins (99) and Chris Liddle (53). Skipper Chris Adams had advanced to 74 when he became one of Kabir Ali's three victims.
Martin-Jenkins, dropped from hard chances on the run to Ray Price and Malik at 60 and 96 respectively, hit a dozen fours and a six over long-on off Gareth Batty before being well caught at point trying to force medium-pacer Mitchell off the back foot. Liddle, after thumping 11 fours in a 62-ball 53, also fell to Mitchell, who had a career-best first-class return.
Mitchell and Moore had negotiated 29 overs when Mushtaq's googly had the latter caught off an inside edge at short leg. Moeen Ali fell cheaply before Mitchell and Hick shored things up until bad light ended play 75 minutes early.
Lancashire, meanwhile, saw Surrey declare on 427 for nine after run-machine Mark Ramprakash struck a stunning 196 before they were all out for 234. Surrey closed on ten without loss.
Durham remain in the title hunt after totalling 321 in reply to Kent's 212 at Canterbury, skipper Dale Benkenstein scoring 117. Kent were limited to 99 for three in their second innings.
