Essex resumed on the third morning on 110-3, just 80 behind, but were soon hit by a burst of 3-8 in 16 balls from Gilchrist. The overnight batters were removed when Charlie Allison fell lbw for 44 and nightwatcher Cook, having resisted for 54 minutes, was caught high at second slip by Rob Yates.
Michael Pepper then fell second ball when he could not resist a half-volley and Webster took a smart low catch at cover.
If Pepper contributed to his own downfall, so did Matt Critchley 18 balls later when he lashed a wide ball from Bamber to point.
Harmer knuckled down defiantly but Ed Barnard defeated Snater’s leg-side swipe to win an lbw decision.
When Keith Barker disturbed debutant Zaman Akhter’s off-stump, Essex were still four behind with the last pair together.
Harmer twice lifted Barnard into the Hollies Stand to take Essex in front and past 200, but then played on to Gilchrist with the lead just 15.
Warwickshire’s second innings reached 14-0 but they then lost three wickets in 22 balls without adding a run. Jamie Porter inflicted the damage in the first innings. This time it was Cook as Alex Davies and Sam Hain edged to second slip either side of Dan Mousley driving to cover.
At 14-3, Webster settled into an innings of the highest quality but support was fleeting as Essex kept breaking through again just as partnerships developed. Stands of 44, 36 and 50 respectively with the Aussie ended when Yates lifted Snater to cover, Barnard edged the same bowler into the cordon and Zen Malik plonked Porter straight into the hands of deep square leg.
Harmer chipped in with the wicket of Jordan Thompson, caught at slip. When Cook completed his 15th first-class five-for when Barker edged behind, it was 188-9 but Bamber (19 not out) and Gilchrist (17) eked out a potentially invaluable 32 from 48 balls before Snater bowled the latter.
Faced with an awkward four overs to bat, Essex survived unscathed with acting captain Cook completing his excellent day with another successful mission as nightwatcher.
