Mushtaq Ahmed collected his sixth five-wicket haul of the season but Sussex will feel they missed the chance to build an impregnable position against the first division strugglers.
The brilliant leg-spinner took his season's haul to 60 with 5-93, helping to reduce the winless Foxes to 154-6 early in the afternoon session.
But Leicestershire's evergreen skipper Phil DeFreitas came to his side's rescue with 103, adding 96 in 27 overs with Jeremy Snape for the seventh wicket before dominating an even more important stand of 69 in 18 overs for the ninth wicket with Charlie Dagnall when his side were 251-8 and really in danger of missing the boat on the best batting surface at Grace Road all season.
It was hardly a surprise that DeFreitas did not emerge to open the bowling a few minutes after losing his middle stump to Robin Martin-Jenkins.
When you are 37, batting for over three hours when the thermometer is nudging 90 degrees is going to take it of you.
It is as a bowler that Leicestershire really need DeFreitas's skill and he will doubtless have to do a lot of work today. Sussex had 16 overs to negotiate last night and they were 51-0 at the close with neither Richard Montgomerie nor Murray Goodwin looking in any trouble.
Sussex's cause was not helped by the absence from their attack for much of the day of Jason Lewry.
The left-armer must have fancied his chances of carrying on where he left off at Arundel last week when he produced his best match figures for two years against Essex.
But after bowling five testing overs with the new ball Lewry had to go off because of a side strain. He returned to bowl one more but was clearly in pain and spent the rest of the day having treatment.
Sussex changed a winning team by bringing in Kevin Innes for Mark Davis but the medium-pacer and Martin-Jenkins struggled to make much impression on such an easy-paced track until Martin-Jenkins wrapped up the innings shortly after 5.30pm by taking two wickets in two balls.
Fortunately, Mushtaq and James Kirtley carried the burden manfully once again, reinforcing the point that so much depends on their ability to stay fit and fresh if Sussex are to maintain their pursuit of leaders Surrey.
Kirtley struck with the second ball of the match when he pinned John Maunders in his crease and he returned in the afternoon to end Snape's resistance with a full-length delivery which kept a shade low.
But, not surprisingly, it was Mushtaq whom the Leicestershire batsmen found as unfathomable as so many other county batting units have in the first half of the season.
His excitable appealing did not go down well with the Grace Road public and when he took the first of two wickets in three balls in the first over after lunch to dismiss Trevor Ward it appeared to be a case of if you appeal long and loudly enough eventually the umpire is going to give in.
Mushtaq came into the attack in the 17th over and ended a stand of 60 for Leicestershire's second wicket with his fifth ball, a top-spinner which Maddy made the fatal mistake of playing back to.
Sussex supporters may remember a superb, career-best 130 Darren Stevens made at Arundel in 1999. The 27-year-old has not lived up to the promise he showed that day and before yesterday he had only passed 50 twice in 13 Championship innings this summer.
So it was a surprise to see Stevens opening the batting instead of in his normal No. 6 slot, especially as Leicestershire had drafted in a specialist opener in Trevor Ward to replace Virender Sehwag who dropped out with a back strain.
But Stevens made a decent fist of his new role, helping Australian Brad Hodge add 47 in 12 overs for the third wicket before Mushtaq struck again. Stevens had just struck his ninth boundary to go to 51 but he overbalanced trying to work the ball through square and Tim Ambrose had the bails off in a flash.
Mushtaq had 2-23 from nine overs at lunch but his best work was still to come.
Straight after the resumption John Steele upheld a leg before appeal which got louder with every stride he took nearer the unfortunate Ward.
Paul Nixon made his intentions clear from the start when he swept his first delivery fine for four. But trying to repeat the shot off the next ball he lost his off stump via a top edge.
Three overs later Mushtaq snared the dangerous Hodge who was well taken low down at silly point by Montgomerie for 47.
DeFreitas cannot have imagined he would be coming out to bat at 2.25pm when he won the toss and it was hard work for him and Snape early on.
Kirtley finally came back to temporarily relieve Mushtaq and broke through in the second over of his spell, bowling Snape with a full-length ball which swung in a touch.
Adams sensibly brought Mushtaq back on at the pavilion end in the 68th over to bowl at the tail and he must have been expecting his side to be batting before tea when Goodwin's direct hit from square leg ran out David Masters after an awful mix-up with DeFreitas.
Leicestershire were 251-8 and, initially at least, Dagnall found Mushtaq hard work. DeFreitas sensed as much and after tea he went on the attack, racing from 56 to 103 in just 12 overs with a succession of lusty blows.
A pulled six which landed in the practice nets and successive boundaries, all in one over from Martin-Jenkins, took him to 99 before he guided the same bowler through point for his 15th four in the 86th over to bring up the tenth century of a career which began 18 summers' ago.
Two balls later he lost his middle stump trying to deposit Martin-Jenkins over square again and Rupesh Amin lasted just one ball before he was castled by a yorker.
Leicestershire 320 all out; Sussex 51 for 0
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article