Greg Smith finished with a career-best 177 as Essex clinched maximum batting points for the first time this season and took a firm grip on the LV= County Championship Division Two match with Gloucestershire at Bristol.
After rain had washed out 25 overs, the visitors extended their first-innings total from an overnight 333 for seven to exactly 400, Smith the last man out having faced 303 balls in a near seven-hour stay at the crease.
Gloucestershire slipped to 41 for three in reply prior to a century stand between Alex Gidman and Hamish Marshall, who hit 63 and 54 respectively.
However, Graham Napier, with 4-72, and Reece Topley, who claimed 3-68, ensured the hosts were reduced to 211 for nine by the close. They required a further 40 to avoid the follow-on.
Rain delayed the start until 1:25pm and then interrupted play after just 10 balls, but the clouds got higher and a resumption came at 1:50pm.
Monty Panesar hit a breezy 22 in a stand of 42 with Smith, who went past his previous best first-class score of 165 not out, made for Derbyshire against Glamorgan at Derby in 2010.
After Panesar had top-edged a catch to fine-leg off David Payne, Tymal Mills helped secure a fifth batting point with 17 before falling to the left-arm spin of Tom Smith.
Smith was finally bowled by Craig Miles to end the innings, but Gloucestershire skipper Michael Klinger's fear that his bowlers had under-performed proved correct.
Chris Dent, Klinger and Gareth Roderick all fell cheaply in the first 11 overs of the home side's reply, Napier taking two of the wickets and Topley one.
Gidman became the first Gloucestershire player to pass 1,000 first-class runs for the season shortly after reaching a half-century off 72 balls, but both he and Marshall had to ride their luck when adding 101 in 24 overs.
Their partnership ended on 142 when Gidman had his middle stump uprooted by Ryan ten Doeschate, having hit 11 fours.
Benny Howell was then run out for 11 by Topley's sharp throw from midwicket after calling Marshall for a quick single.
Marshall was dropped twice in the slips by Owais Shah and Gautam Gambhir on 44 and reached his half-century off 86 balls, with eight fours, before getting a sharp delivery from Topley and edging a catch to wicketkeeper James Foster.
Smith followed, edging to Shah at first slip off Napier to leave Gloucestershire 172 for seven, still 79 runs away from avoiding the follow-on.
A lifting delivery from Topley accounted for Gidman and Payne was yorked by Napier for a duck, but a flurry of boundaries from Miles brought the home side a welcome batting point.