Leicestershire 252 and 99 for 1 (Horton 53*) need a further 131 to beat Sussex 173 and 308 (Ackermann 5-69, Taylor 4-75)
Leicestershire were on course to claim their first County Championship win over Sussex for 17 years after making a positive start to their pursuit of a target of 230 at Hove. Skipper Paul Horton made an unbeaten 53 to take his side to 99 for 1 when rain arrived at tea and play was abandoned for the day at 5.35pm with Leicestershire still needing 131.
Debutant Hasan Azad helped Horton put on an unbroken 72 for the second wicket after David Wiese had pinned Ateeq Javid lbw with an in-swinger for 11.
Horton reached his half-century off 79 balls with seven fours but he needed a check by the Leicestershire physio after ducking into a Chris Jordan's bouncer which struck him on the helmet.
Their victory charge had been set up earlier in the day by offspinner Colin Ackermann, who finished with career-best figures of 5 for 69, and seamer Tom Taylor, who claimed four more victims to add to his six in the first innings for a match haul of 10 for 122, also a career-best.
Sussex had resumed on 211 for 2 - a lead of 132 - and in good batting conditions must have been confident of setting the visitors a target of more than 300. Instead, they lost their last eight wickets in adding a further 97, three of them for 11 balls at a cost of two runs during the morning session.
Taylor made a breakthrough in the first over when Stiaan van Zyl (41) feathered an outswinger to Lewis Hill, one of four catches for the Foxes' wicketkeeper.
Luke Wells and Harry Finch added 23 with few alarms before Sussex's middle order was wrecked by Taylor and Ackermann. Wells lost patience on 48 and also lost his middle stump aiming an expansive drive at Taylor. In his next over Taylor had Wiese leg-before to a ball which kept a touch low while Sussex captain Ben Brown was lbw playing back to Ackermann for his second duck of the match.
Sussex rebuilt through Finch and Jordan, who added 49 for the seventh wicket, but when it appeared that they were wresting back the initiative Ackermann completed his five-for with two wickets in three balls thanks to athletic catches at short leg by Azad. Jordan was held off a top-edged sweep and Ollie Robinson became the sixth Sussex batsman to go for a duck in the match, again off a misjudged sweep.
The innings ended shortly after lunch. Danny Briggs was caught behind off Taylor's outswinger and Finch, with only last man Mir Hamza for company, drove at Chris Wright and Hill did the rest behind the stumps.