Somerset 53 for 3 (Abell 13*, Klein 2-24) trail Leicestershire 233 (Hill 68, Overton 3-39) by 180 runs
Lewis Hill posted his fourth half-century in as many innings but Leicestershire were made to struggle after opting to bat first in their LV=Insurance County Championship match against Somerset.
Australian Test opener Marcus Harris could make only 19 on his debut in English domestic cricket as Leicestershire were bowled out for 233, below par even though they were at one stage 74 for 5.
Yet what looked like being Somerset's day was tempered by a poor start to their reply that saw them lose their first three wickets for 39 before closing on 53 for 3.
Craig Overton took 3 for 39, England spinner Jack Leach 2 for 26 and Lewis Gregory 2 for 39 as Somerset's strong attack returned to something much more akin to its regular potency following last week's surprise defeat to West Country rivals Gloucestershire.
But after a loose first over that conceded 17 runs, Chris Wright gave the home side a fillip as Tom Lammonby was lbw after failing to go through with his intended stroke, and then Dieter Klein, producing some good swing, had Tom Banton leg before and James Hildreth caught at second slip.
Earlier, Harris and Hassan Azad made a confident start as they teamed up for the first time after Colin Ackermann won the toss, but four wickets in the second hour swung the opening session squarely in Somerset's favour as Leicestershire slipped from 40 without loss to 68 for 4 at lunch.
Harris caught the eye with a couple of nicely timed off drives but was caught behind off the bottom edge when Gregory tempted him with some width outside off stump.
Gregory claimed his second success with an lbw verdict against Harry Dearden, who looked unlucky, before Marchant de Lange had Ackermann plumb in front .
Azad, fresh from a fine unbeaten 144 at the Oval, looked in sound order in reaching 36 but then gave his wicket away in the last over of the session, chasing a short and wider ball from Somerset skipper Tom Abell that he could only help through to the 'keeper.
Leicestershire's troubles continued after lunch as Harry Swindells was caught at first slip via second as he tried to get out of the way of a short ball from Overton, leaving them 74 for 5.
But Hill, strong on the off side, hit 10 boundaries before Overton had him caught behind square on the leg side for 68, top-edging an attempt to clip the ball off his legs.
He added 59 with Ben Mike before the latter was leg before to Leach's first ball and 47 for the seventh wicket with Callum Parkinson, who finished unbeaten on 27 after surviving a chance on seven, and useful runs from the tail swelled Leicestershire's total, the last three wickets adding 48.