Chelmsford City shocked League One side Colchester United to reach the second round and win the first encounter between the Essex sides for 44 years.
The Blue Square Bet South team took the lead when Donovan Simmonds collected Jamie Slabber's flick-on and superbly lobbed Mark Cousins from 25 yards.
Simmonds added his second by poking home Richard Brindley's long ball.
Michael Rose pulled one back from a free-kick but Slabber's tidy finish sent the home crowd into raptures.
The last time the sides met was an FA Cup second-round tie in January 1968, which Colchester won 2-0, meaning this Essex derby had been eagerly anticipated since it was drawn out of the hat.
And despite Colchester's early possession, the home side were rarely troubled at the back, belying their position 61 places below the U's in the football pyramid.
Following Simmonds's opener, Anthony Wordsworth should have levelled, but he failed to make contact with Sanchez Watt's free-kick with the goal gaping.
Former Coventry youngster Simmonds, 24, showed his bravery for the second, taking a heavy challenge from Cousins while touching the ball past the keeper.
Rose made it interesting with his sweetly hit free-kick and Stuart Searle had to pull off a sharp save from Jabo Ibehre.
But the Clarets were able to celebrate an upset they will never forget when Slabber lashed in Simmonds's cut-back.
VIEWS FROM THE DRESSING ROOM
Colchester United Manager Joe Dunne told BBC Essex:
"It's probably the worst moment of my football career because I'm in charge - It's a dark day.
"It's a steep learning curve, but I relish the challenge and seeing how I come out of it.
"It's a setback, that's all it is. We've had them before and we'll have them again. Unfortunately, it's against a local rival and congratulations to Chelmsford, they fully deserved it.
"The effort, the commitment, the attitude, the tenacity and the bravery of Chelmsford have got them into the next round and I would not begrudge them that. They've made history."
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Live Text Commentary
Full Time The referee blows for the end of the match.90:00 +3:55
Short corner taken by Freddie Sears from the right by-line, Gavin Massey takes a shot. Stuart Searle makes a save.90:00 +3:39
Jamie Slabber is caught offside. Michael Rose takes the free kick.90:00 +0:35
Unfair challenge on Jabo Ibehre by Anthony Cook results in a free kick. Direct effort from the free kick comes in from Michael Rose, save by Stuart Searle.90:00 +0:18 Booking
Booking Anthony Cook receives a caution for unsporting behaviour.90:00 +0:06 Booking
Booking Booking for Donovan Simmonds for unsporting behaviour.88:56
Donovan Simmonds provided the assist for the goal.88:56 Goal scored
Goal! - Jamie Slabber - Chelmsford 3 - 1 Colchester Jamie Slabber grabs a goal from inside the area to the top right corner of the goal. Chelmsford 3-1 Colchester.87:24
Anthony Cook decides to take a short corner.86:50
The assistant referee signals for offside against Jabo Ibehre. Stuart Searle takes the indirect free kick.85:58
Corner taken by Anthony Cook from the left by-line, Kenny Clark delivers the ball, save by Mark Cousins.85:41
Anthony Cook takes a corner.85:23
David Rainford takes a shot. Save by Mark Cousins.82:28
Jabo Ibehre takes a shot. Save made by Stuart Searle.80:30
Short corner taken by Freddie Sears, Shot on goal by Magnus Okuonghae from inside the box goes harmlessly over the target.78:56
The ball is swung over by Donovan Simmonds, Max Cornhill takes a shot. Save made by Mark Cousins.77:43
Free kick awarded for an unfair challenge on Sam Corcoran by Gavin Massey. Stuart Searle restarts play with the free kick.75:32
Centre by Freddie Sears, save by Stuart Searle.73:33 Substitution
Substitution Sam Corcoran joins the action as a substitute, replacing Ishmael Welsh.72:40
The ball is sent over by Anthony Wordsworth, save by Stuart Searle.
Freddie Sears takes a inswinging corner.71:09
Foul by Max Cornhill on Marcus Bean, free kick awarded. Magnus Okuonghae takes the free kick.70:39
The assistant referee flags for offside against Jabo Ibehre. Indirect free kick taken by Stuart Searle.69:54 Goal scored
Goal! - Michael Rose - Chelmsford 2 - 1 Colchester Michael Rose scores a goal direct from the free kick from a long way out to the top left corner of the goal. Chelmsford 2-1 Colchester.68:45
Free kick awarded for a foul by Aiden Palmer on Marcus Bean.67:22 Substitution
Substitution Gavin Massey comes on in place of Ian Henderson.67:22 Substitution
Substitution Clinton Morrison replaces Craig Eastmond.66:17
The referee blows for offside. Tom Eastman restarts play with the free kick.64:26
David Rainford challenges Craig Eastmond unfairly and gives away a free kick. Mark Cousins takes the indirect free kick.62:01
Assist on the goal came from Richard Brindley.62:01 Goal scored
Goal! - Donovan Simmonds - Chelmsford 2 - 0 Colchester Donovan Simmonds scores a headed goal from just inside the penalty area. Chelmsford 2-0 Colchester.60:57
Craig Eastmond decides to take the corner short, Headed effort from inside the penalty area by Tom Eastman misses to the right of the target.60:46
The ball is sent over by Michael Rose.59:41 Substitution
Substitution Freddie Sears joins the action as a substitute, replacing Sanchez Watt.57:57
Ian Henderson produces a cross, Kenny Clark manages to make a clearance.56:54
The offside flag is raised against Jabo Ibehre. Stuart Searle takes the indirect free kick.56:01
The ball is crossed by Ishmael Welsh, Michael Rose makes a clearance.54:00
Corner from right by-line taken by Sanchez Watt.53:38
The referee blows for offside against Jamie Slabber. Indirect free kick taken by Tom Eastman.52:07
Ishmael Welsh gives away a free kick for an unfair challenge on Marcus Bean. Sanchez Watt produces a shot on goal direct from the free kick.51:30
Inswinging corner taken by Sanchez Watt, Justin Miller manages to make a clearance.50:22
Anthony Cook takes a shot.49:15
Marcus Bean sends in a cross, clearance by Ishmael Welsh.47:06
Anthony Cook fouled by Sanchez Watt, the ref awards a free kick. Free kick taken by Stuart Searle.46:06
The ball is crossed by Michael Rose.45:01
The referee gets the second half underway.45:00 +1:06 Half time
Half Time The half-time whistle blows.45:00 +0:34
The referee blows for offside against David Rainford. Free kick taken by Mark Cousins.43:50
Anthony Wordsworth challenges Richard Brindley unfairly and gives away a free kick. Free kick taken by Richard Brindley.42:55
David Rainford sends in a cross, clearance by John White.41:53
Sanchez Watt takes a shot. Kenny Clark gets a block in.40:37
Free kick awarded for an unfair challenge on Anthony Cook by Craig Eastmond. Justin Miller restarts play with the free kick.40:10
The ball is swung over by Aiden Palmer, save made by Mark Cousins.39:22
Effort on goal by Jabo Ibehre from long range goes harmlessly over the bar.38:56
The official flags Donovan Simmonds offside. Tom Eastman restarts play with the free kick.38:18
Handball by Craig Eastmond. The free kick is swung in right-footed by Anthony Cook.36:00
Free kick awarded for an unfair challenge on Donovan Simmonds by Michael Rose. Free kick taken by Richard Brindley.31:50
Ian Henderson delivers the ball.31:15
Aiden Palmer takes a shot. Mark Cousins makes a save.29:08
Anthony Cook takes a inswinging corner.28:53
The ball is delivered by Aiden Palmer.26:21
Michael Rose produces a cross.26:03
Michael Rose sends in a cross, David Rainford manages to make a clearance.23:51
Anthony Cook concedes a free kick for a foul on Michael Rose. Strike comes in from Michael Rose from the free kick, blocked by Stuart Searle.22:18
Jamie Slabber provided the assist for the goal.22:18 Goal scored
Goal! - Donovan Simmonds - Chelmsford 1 - 0 Colchester Donovan Simmonds grabs a goal from outside the penalty area to the bottom right corner of the goal. Chelmsford 1-0 Colchester.19:52
A cross is delivered by Anthony Cook.19:14
Tom Eastman fouled by Jamie Slabber, the ref awards a free kick. Tom Eastman takes the free kick.18:31
Aiden Palmer fouled by Ian Henderson, the ref awards a free kick. Free kick taken by Kenny Clark.17:51
Richard Brindley crosses the ball, Tom Eastman makes a clearance.16:29
Free kick awarded for a foul by Craig Eastmond on Ishmael Welsh. Anthony Cook restarts play with the free kick, Max Cornhill takes a shot. Save by Mark Cousins.15:26
Corner from left by-line taken by Sanchez Watt.14:43
A cross is delivered by Sanchez Watt, Anthony Wordsworth takes a shot. Save made by Stuart Searle.14:08
The ball is delivered by John White, clearance by Justin Miller.13:21
Sanchez Watt crosses the ball.11:00
Shot from just outside the box by Anthony Wordsworth goes over the crossbar.9:29
The ball is crossed by Anthony Wordsworth, Justin Miller manages to make a clearance.8:38
Inswinging corner taken by Sanchez Watt. Kenny Clark makes a clearance.8:07
The assistant referee signals for offside against Donovan Simmonds. Magnus Okuonghae takes the free kick.7:49
The ball is swung over by Marcus Bean, clearance made by Kenny Clark.7:29
A cross is delivered by John White.6:55
Jabo Ibehre takes a shot. Save made by Stuart Searle.4:00
Richard Brindley takes a shot.3:41
The ball is sent over by Anthony Cook.1:56
Inswinging corner taken by Jabo Ibehre, Kenny Clark makes a clearance.0:44
Ishmael Welsh crosses the ball, save by Mark Cousins.0:08
The ball is delivered by Anthony Cook, save made by Mark Cousins.0:00
The referee gets the game underway.
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