They responded by bowling Sussex out for just 154 to set themselves a target of 253 and then openers Alex Davies and Keaton Jennings got their second innings off to a flying start with a stand of 102 in 20 overs.
Davies led the way with a 59-ball 73, with ten fours and a pulled six over square leg off Henry Crocombe before he was bowled by Stuart Meaker. And Jack Carson gave his side a lifeline with the late wicket of former Sussex player Luke Wells, who was lbw padding up. At the close of the third day Lancashire were 124 for two and need another 129 for victory.
Lancashire started the third day on 193 for six at the 1st Central County Ground,135 runs behind, and lost their last four wickets for 37 runs in the space of 45 minutes.
Sussex broke through in the third over of the morning when Josh Bohannon, who had just on-driven Henry Crocombe for a fine four, was lbw to a Jamie Atkins delivery that moved into him.
Lancashire had added just ten more when they lost their second wicket of the session when Tom Bailey had his leg stump plucked out by a well pitched-up delivery from Crocombe for three; 215 for eight. Meaker brought the curtain down on the Lancashire innings with two wickets in successive overs. First, he pinned Danny Lamb for 27 and then he bowled a short, lifting delivery to Matt Parkinson who gloved it to the keeper.
Lancashire were all for 230 in 98.2 overs. Meaker finished with figures of three for 22, his best return for Sussex. But the morning continued to belong to the bowlers and by lunch Lancashire had muscled themselves back in the game by reducing Sussex to 37 for three.
Aaron Thomason, perhaps unsettled by a nasty, rearing ball from Lamb two balls earlier, was caught at first slip by Wells. Without addition Sussex lost the in-form Tom Haines, lbw to Bailey for 19. And Bailey struck again in his next over with the key wicket of Stiaan van Zyl, caught at second slip by Liam Livingstone. The only meaningful resistance came from Delray Rawlins, who made 45, with five fours, almost one third of the Sussex total.