Lancashire 322 (Vilas 90, Croft 63) and 96 for 3 (Davies 54) lead Leicestershire 409 for 8 (Slater 172, Ackermann 94, Azad 58) by nine runs
Ben Slater hit a career-best 172 and Colin Ackermann 94 as Leicestershire declared with a first-innings lead of 87 before taking three early wickets as opponents Lancashire closed the third day just nine runs ahead in the Bob Willis Trophy match being played at Blackfinch New Road.
Keaton Jennings went caught at third slip off Chris Wright for 8, the ball looping off an inside edge and his pads, Josh Bohannon was leg before wicket to a full delivery from Ben Mike for 3, and Alex Davies leg before for 54 missing a pull at a delivery from left-arm spinner Callum Parkinson that went on with the arm to give the Foxes real hope of forcing victory on the final day.
Slater, signed by Leicestershire on a two-week loan from Nottinghamshire, shared in a partnership of 165 with Ackermann, a third-wicket record for Leicestershire against Lancashire, beating the 163-run partnership between James Bradshaw and Norman Armstrong at Leicester's old Aylestone Road ground in 1929.
Ackermann was positive from the start when his side resumed on 183 for 2, looking to get forward where possible against an inexperienced bowling attack including three men making their first-class debuts in seamers Ed Moulton and George Balderson, and left-arm spinner Tom Hartley.
All bowled straight and to their fields, however, and on a good, dry but slightly slow pitch, Ackermann and Slater found it hard to work the ball to the boundary. Slater kept the scoreboard moving with singles as he worked his way towards 150, going in to lunch on 143 off 318 balls, while Ackermann hit seven fours in reaching 50 off 88 deliveries. Only one chance was created, when Ackermann, on 47, drove a delivery from Balderson that stopped a little in the pitch back towards the young bowler, who was unable to hold the catch very low to his left.
It was a different story after the interval as Leicestershire looked to secure a fourth batting bonus point. Having passed 150, Slater lofted Tom Bailey for consecutive sixes over long-on, but a third attempt landed in the hands of Bohannon at deep mid-off.
George Rhodes came and went quickly in the search for quick runs, driving Bailey to Dave Vilas at cover, but Ackermann, on 94, looked certain to reach a century of his own until he was called through for an unlikely second run by Tom Taylor and failed to beat Jennings' throw from the midwicket boundary.
When Taylor went lbw hitting across the line at Balderson and Harry Swindells was bowled trying to improvise against Hartley's left-arm spin, Leicestershire had lost five wickets for 43 runs, but Mike, Klein and Parkinson saw them past 400 before Ackermann declared to ensure the Foxes were able to bowl before tea.
Neither Jennings nor Davies were troubled during the seven overs they did bowl before the break, but Jennings' unfortunate dismissal, followed by those of Bohannon and Davies, means much will depend on Lancashire's in-form captain Dave Vilas, who was unbeaten on 7 at the close.
Before play began, match umpire Alec Swann confirmed Leicestershire seamer Klein had been handed a three-point penalty and a reprimand after being adjudged to have committed a level two offence under Law 43, throwing the ball at another player in an inappropriate and dangerous manner.
The incident occurred on the second day of the game, when Klein threw the ball at the stumps but hit Lancashire batsman Danny Lamb on the foot.