Worcestershire captain Daryl Mitchell became the second player to reach 1,000 championship runs for the season before Leicestershire's bowlers pegged the Division Two leaders back to 317-9 on day one at New Road.
Everything was going well as Mitchell (90) and new partner Richard Oliver (78) made trouble-free progress in an opening stand of 163, but there was surprise in store when paceman Nathan Buck led the Leicestershire revival by taking 3-1 in 11 balls.
Spinners James Sykes and Dan Redfern shared the spoils as the bottom-of-the-table visitors - without a championship win in 26 matches - claimed 6-95 runs between lunch and tea.
Sykes (3-72) added two more in the final session, mostly importantly the lbw dismissal of Tom Kohler-Cadmore for 41 after the teenager after steadied Worcestershire in a partnership of 44 in 21 overs with Shaaiq Choudhry.
Choudhry, essentially brought in to fill Moeen Ali's role as a spin bowler, showed his value as a lower-order batsman, making 40 not out from 107 balls, and Saeed Ajmal (20) drove Buck for six before he was dislodged by a lifter from Charlie Shreck.
There was no action on day one at Colchester between Essex and Hampshire.
Play was called off shortly before 3pm after consistent heavy rainfall in the area.