Already nine points adrift of Manchester United, Chelsea desperately needed to win but it was Arsenal, in the unlikely form of Mathieu Flamini who hit the first goal 11 minutes from time before Essien's remarkable 25-yard right-footed piledriver levelled the scores and the match.
Arsenal's first chance came via a Robin van Persie free-kick on eight minutes but the Dutchman's effort went straight into the Chelsea wall.
Chelsea striker Andriy Shevchenko hit a fine strike on the Arsenal goal on 15 minutes. Unluckily for the Ukraine hitman, Jens Lehmann was well positioned to block the effort.
Two minutes later and it was the turn of Germany captain Michael Ballack to let fly from 25 yards. This time the right-footed strike beat Lehmann but also the goal.
Frank Lampard could have put the champions ahead 30 seconds later but his left-footed half-volley from just inside the Arsenal area bounced back from Lehmann's left upright.
Ashley Cole was booked by Alan Wiley for a late challenge on Aleksandr Hleb which caused the Chelsea bench to rise up in unison with Jose Mourinho crossing on to the pitch to protest.
A long-range effort, again from van Persie, failed to trouble Henrique Hilario in the Chelsea goal on 25 minutes.
A fine Chelsea break on 32 minutes involving Geremi wide on the right saw his drive into the area touched on by Didier Drogba into the path of the on-rushing Essien. But the midfielder toe-poked the ball, under pressure from Philippe Senderos, over the bar.
Van Persie whipped over a fine cross on 39 minutes but Flamini saw his header go over the Chelsea bar.
Arsenal had a stroke of luck on 38 minutes when Lehmann made a hash of a corner and the ball fell to Essien whose left-foot drive was kicked off the right post by Cesc Fabregas.
Emmanuel Adebayor had the first chance of the second half but his snatched shot drifted wide of the Chelsea goal.
Van Persie saw his header from the impressive cross from Adebayor go over the bar on 49 minutes.
A booking for Flamini for a foul on Frank Lampard on 55 minutes left Chelsea with a free-kick from 25 yards. But it was a limp effort by Geremi and the ball hit the Arsenal wall.
A fine 40-yard run by Adebayor resulted in a van Persie shot on target but straight into Hilario's midriff.
Mourinho decided on a change of tactics by bringing on wingers Shaun Wright-Phillips for Geremi and Arjen Robben for Shevchenko, but not before pantomime season hit full flow on 53 minutes.
First Drogba was livid that he was not given a penalty from a heavy challenge by Senderos. Lehmann then pushed Drogba who fell to the ground theatrically. Drogba then shoved Lehmann and he went down like a sack of potatoes. Wiley eventually decided to book both of them.
Robben was soon in the action and on 72 minutes he took full advantage of a poor clearance by Senderos but Lehmann blocked well.
Seconds later and another Robben shot flashed across the Arsenal goal but missed the target.
The north Londoners took the lead following sustained Chelsea pressure with 11 minutes remaining.
Excellent approach play saw Hleb square the ball across the edge of the Chelsea area and up stepped Flamini to ram home a fierce drive into the corner despite Hilario getting a touch to it.
Drogba had a fine chance to equalise three minutes later when a Claude Makelele through pass was chested on by the Ivory Coast man who slid the ball past Lehmann but also just past the Arsenal post.
But the champions produced a moment of magic and a counter-attack saw the ball move across the pitch with Lampard setting up Essien, who 25 yards out, sent an unstoppable right footer into the top left-hand corner of the net with Lehmann helpless to get anywhere near it.
Essien could have notched up the winner in stoppage time but his right-footed shot hit the underside of the crossbar and bounced away to safety.
Lampard then hit the post in the dying seconds as Arsenal hung on for a point.