Twenty wickets fell on day one of the Vitality County Championship match at Taunton with Essex rolling Somerset for 128 after they had been bundled out for 156.
Somerset seamer Migael Pretorius claimed 4-36 as the home side impressed after electing to bowl, with Tom Westley (43) the only Essex batter to pass 25.
But Jamie Porter (5-37) and Sam Cook (5-38) then shredded the hosts as Essex earned a first-innings lead of 28, one they extended to 34 by stumps as nightwatchman Cook (4no) saw out a sole over in the company of Dean Elgar (0no).
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Each of the wickets on the day fell to seam bowling.
Rain affected the matches elsewhere but Kent's Joey Evison (50no) made his third half-century of the season as they reached 203-7 against Lancashire at Emirates Old Trafford, in a game being shown live on Sky Sports.
Evison and Grant Stewart (45) came together at 129-3, after George Balderson had taken three wickets in 28 balls, and proceeded to put on 69 for the seventh wicket.
Division One scorecards
Division Two scorecards
In Division Two, England bowler Ollie Robinson took two wickets to help put Sussex into a strong position at Derbyshire.
Robinson bowled five consecutive maidens either side of lunch and claimed 2-48 as Derbyshire reached 189-8 before rain prevented any further play - Luis Reece top scored with 50 from 78 balls and Aneurin Donald hit nine fours in his 44.
Glamorgan opener Billy Root was dropped on six by older brother Joe and went on to score 51 against Yorkshire as the Welsh side made 109-4 in 41 overs at a rain-hit Headingley.
Day one between Middlesex and Leicestershire at Lord's was entirely wiped out by the rain.
Watch day two of Lancashire vs Kent, live on Sky Sports Cricket and Sky Sports Mix from 10.50am on Saturday.
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