Essex 298 (ten Doeschate 78, Browne 61, Milnes 4-46) and 0 for 0 need 202 runs to beat Kent 387 and 112 (Harmer 4-35)
Simon Harmer showed glimpses of his 2019 form to snatch four wickets and set up a pulsating final day of Essex's Bob Willis Trophy clash with Kent.
Former South Africa spinner Harmer, who took 71 wickets last season, had been targeted in the first innings and had gone 26 overs without a wicket before pinching two late scalps.
It means Essex, who earlier saw Ryan ten Doeschate score 78, will require 202 to win on the last day at the Cloudfm County Ground, Chelmsford.
This time around, they fell to 36 for 3 in 21 overs, before continuing the slide.
Porter, who had taken 4 for 107 earlier in the match, got the ball rolling when Daniel Bell-Drummond edged behind to Adam Wheater.
Kent debutant Jack Leaning was on a pair after his first innings duck, and narrowly avoided the calamity when his edge fell just short of Sir Alastair Cook at first slip. However, the former Yorkshire batsman only managed six before Sam Cook pinned him lbw.
Robinson was dropped on 13 at short leg by Varun Chopra, only to edge Porter to Harmer after a 50-ball 14. Harmer then dismissed Kuhn and Darren Stevens, who both tried to play rare attacking shots, but only picked out Nick Browne and Tom Westley at deep midwicket and long-on respectively.
Grant Stewart quickly followed, caught behind off Porter, before Harmer had Marcus O'Riordan lbw. Jordan Cox had provided resilience with a 29 off 116 balls but Cook produced a brilliant in-ducker to break his defences, before he had Hamidullah Qadri nicking behind, O'Riordan, Cox and Qadri all departing with the score on 100.
Matt Milnes was the last man to fall as he picked out Feroze Khushi on the legside boundary - Kent rolled for 112, losing their last six wickets for 26 runs. Browne and nightwatchman Porter faced one wicketless, and runless, over from Milnes to end the day.
Earlier, ten Doeschate collected his 79th first-class half-century, while also raising money for the Lord's Taverners. The Holland international is one of seven batsmen who are donating money to the Lord's Taverners for every run they score this summer - with six bowlers helping to raise money through wickets.
Playing in his 17th season with Essex, ten Doeschate used that experience to carefully make his way to his 79th first-class fifty on an uncharacteristically sluggish Chelmsford pitch.
Wheater and ten Doeschate needed almost 25 overs to bring up the 50 stand for the sixth wicket, while it took the latter 105 balls to score his first boundary of the match - however, the cover drive was worth the wait.
Wicketkeeper Wheater departed when he was run out by Kuhn at midwicket after ten Doeschate had turned down a single to end the 69-run partnership.
Ten Doeschate, on his 189th first-class appearance, hit O'Riordan for a six over midwicket before moving to his milestone from 122 balls with a dink to third man.
Harmer scored 29 in a 68-run stand with ten Doeschate, before he was plumb in front to O'Riordan just before a post-lunch slump saw the Essex tail only add 18 runs for the last three wickets, with Milnes grabbing all three scalps.
Ten Doeschate fell when he struck to Leaning at point, before Sam Cook pulled to midwicket and Quinn edged to second slip in successive balls - Essex falling to an 89-run first-innings deficit.