Leicestershire 112 for 2 (Ackerman 61*) trail Sussex 438 for 8 dec (Burgess 101*, Wright 88, Ishant 66, Brown 64) by 326 runs
A fine century from Michael Burgess, the second of his career, helped Sussex to a formidable first innings score at the Fischer County Ground before Colin Ackermann, with an unbeaten half-century, led a spirited Leicestershire reply.
Burgess and Ishant Sharma compiled a partnership of 153 for Sussex's eighth wicket, batting through the morning session without being parted.
Burgess, who began his career at Leicestershire, was first to his 50, twice hitting left-arm spinner Callum Parkinson over midwicket for six as he sought to accelerate the scoring rate.
India Test bowler Ishant was equally positive as he registered a maiden first-class half-century, leaving his previous career best score of 31 well behind and he would later follow it with two wickets.
Ishant, who has played 81 Tests and 80 ODIs, clearly relished his battle with Leicestershire's own international bowler Mohammad Abbas. Abbas was convinced he had Ishant leg before on 34, but other than that neither batsman gave a chance as the partnership passed three figures.
Sharma was finally dismissed for 66, attempting to loft offspinner Ateeq Javid for a straight six, but failing to clear Gavin Griffiths at long-off.
"I think I got my highest previous score in a Test match, so I'm pretty happy - I wanted to do as well as I could for the team. Every bowler loves to have a bat, and in internationals you don't get that many opportunities, especially for India, so I was looking forward to having an opportunity.
"I've been nightwatchman for India for four years now, so I'm used to the role. Michael [Burgess] and I just batted. I didn't get nervous when I got close to 50, I wasn't really thinking about it, just staying in my space.
"My main job is to take wickets, so I was probably more pleased about that. The wicket is a bit on the slow side, with more bounce from the top end. It's good to get used to the conditions, and the soft grounds, I'm getting a lot of benefit from that."
Burgess had a fortunate escape on 98, pulling a delivery from Parkinson to midwicket, where Michael Carberry got both hands to the ball above his head but could not hold the chance. He went to his century off 146 balls, hitting five fours as well as the two sixes, before Sussex captain Ben Brown declared.
Buoyed by his success with the bat, Ishant then made an early breakthrough with the ball when he trapped Leicestershire opener Paul Horton leg before with a full delivery. Carberry, defending with purpose and real determination, and the in-form Ackermann saw off the new ball, but Ishant returned to have Carberry adjudged leg before, half-forward to an in-swinger.
Sussex should have had a third wicket when Ackermann turned a David Wiese delivery straight to midwicket, only for Luke Wright, looking into the sun, to fail to hold a straightforward chance.