Crawley capitalised on defensive errors to defeat Sheffield United and dent the Blades' automatic promotion hopes.
The hosts hit the woodwork either side of half-time through efforts from Ryan Flynn and captain Michael Doyle.
And they were made to pay when Paul Hayes robbed United defender Neill Collins to allow former Blades loanee Billy Clarke to fire home.
Hayes then seized upon Harry Maguire's hesitation on the edge of the box to slide home the second and seal victory.
The result leaves Sheffield United six points off second-placed Bournemouth with two games in hand.
VIEWS FROM THE DRESSING ROOM
Sheffield United manager Danny Wilson told BBC Radio Sheffield:
"We've been done by a couple of mistakes, from two boys in particular that have been outstanding for us the last couple of seasons.
"There were good chances in the game, hitting the post. We've been quite unlucky in that respect following things through - not getting the ball in the back of the net has been our problem recently as we well know.
"The saving grace - we've had a few other results that have gone our way and they've done the same as us, so all it does is knock us down by a game.
"Lets hope if we've have had any small mercies it'll be the same for the next day or two."
Crawley Town manager Richie Barker told BBC Sussex:
"It's a proud moment for me, but a fantastic achievement for the players and the football club and thoroughly deserved I thought tonight.
"They're big, they're strong and have a lot of experience and put us under pressure, and I thought our two centre-halves handled it extremely well.
"Sometimes when you play against a team who are going to be big and strong, you then get sucked into doing the same thing back but to be fair, we didn't and passed it very well."
Live Text Commentary
Full Time The referee ends the match.90:00 +3:09
Callum McFadzean challenges Dannie Bulman unfairly and gives away a free kick. Direct free kick taken by Dannie Bulman.90:00 +1:47
The assistant referee signals for offside against Chris Porter. Indirect free kick taken by Paul Jones.90:00 +1:19
Corner taken left-footed by Barry Robson from the left by-line, Mat Sadler makes a clearance.90:00 +0:16
Shot from long range by Barry Robson misses to the right of the goal.89:26
The ball is crossed by Danny Higginbotham, Nicky Adams gets a block in.89:07
Unfair challenge on Ryan Flynn by Mike Jones results in a free kick. Free kick taken by Kevin McDonald.87:43 Substitution
Substitution Sergio Torres goes off and Aiden O'Brien comes on.85:14
Clearance by Mat Sadler.85:14 Substitution
Substitution Mark Connolly replaces Billy Clarke.85:14
Outswinging corner taken left-footed by Barry Robson,84:59
Chris Porter takes a shot. Save made by Paul Jones.83:38 Goal scored
Goal! - Paul Hayes - Sheff Utd 0 - 2 Crawley A goal is scored by Paul Hayes from deep inside the penalty box to the bottom right corner of the goal. Sheff Utd 0-2 Crawley Town.82:46 Substitution
Substitution Michael Doyle goes off and Barry Robson comes on.82:16
Corner taken right-footed by Ryan Flynn.81:53
Callum McFadzean takes a shot. Save made by Paul Jones.80:24
Connor Essam concedes a free kick for a foul on Dave Kitson. Harry Maguire produces a strike on goal direct from the free kick.79:42
Free kick awarded for an unfair challenge on Ryan Flynn by Billy Clarke. Matthew Hill restarts play with the free kick.79:15
The ball is crossed by Nicky Adams, Matthew Hill manages to make a clearance.78:20 Booking
Booking Booking for Dave Kitson for dissent.
Dave Kitson concedes a free kick for a foul on Paul Hayes. Free kick taken by Paul Jones.77:44
Paul Hayes is flagged offside by the assistant referee. Free kick taken by Matthew Hill.76:31
The assist for the goal came from Paul Hayes.76:31 Goal scored
Goal! - Billy Clarke - Sheff Utd 0 - 1 Crawley Billy Clarke finds the back of the net with a goal from inside the area to the bottom right corner of the goal. Sheff Utd 0-1 Crawley Town.72:50
Chris Porter produces a header from deep inside the six-yard box that clears the crossbar.71:25
Centre by Mat Sadler.70:43
Free kick awarded for an unfair challenge on David Hunt by Callum McFadzean. Direct free kick taken by David Hunt.69:46 Substitution
Substitution (Crawley Town) makes a substitution, with Paul Hayes coming on for Jamie Proctor.69:46
Dave Kitson is flagged offside by the assistant referee. Free kick taken by Paul Jones.67:50
Joe Walsh challenges Chris Porter unfairly and gives away a free kick. Michael Doyle has a direct shot on goal from the free kick.67:41
The ball is delivered by Nicky Adams, save by George Long.66:59
Mike Jones takes a shot. Harry Maguire gets a block in.65:08 Substitution
Substitution Callum McFadzean comes on in place of Jamie Murphy.65:08 Substitution
Substitution Chris Porter on for Jonathan Forte.64:13
Unfair challenge on Nicky Adams by Michael Doyle results in a free kick. Free kick taken by Dannie Bulman.63:16
Shot from just outside the box by Nicky Adams goes over the bar.62:12
Short corner taken by Nicky Adams from the right by-line.62:01
Jamie Proctor takes a shot. Harry Maguire gets a block in.61:08
Danny Higginbotham produces a cross, Mat Sadler manages to make a clearance.59:37
A cross is delivered by Jamie Murphy, Mike Jones makes a clearance.57:04
Billy Clarke takes a long range shot clearing the bar.56:20
Sergio Torres takes a shot. Save made by George Long.55:22
Jamie Murphy gives away a free kick for an unfair challenge on Mat Sadler. The free kick is delivered right-footed by Nicky Adams from left channel, clearance made by Neill Collins.52:30
Unfair challenge on Kevin McDonald by Mike Jones results in a free kick. Strike comes in from Ryan Flynn from the free kick, save made by Paul Jones.50:12
The ball is sent over by Danny Higginbotham, clearance made by Mat Sadler.49:39
Centre by Ryan Flynn, save made by Paul Jones.47:47
Jamie Murphy sends in a cross, Effort from outside the box by Michael Doyle hits the post.45:01
The second half begins.45:00 +1:36 Half time
Half Time The referee calls an end to the first half.44:43
The ball is delivered by Nicky Adams, Billy Clarke takes a shot. George Long makes a brilliant save.42:44
Mike Jones takes a shot. Save by George Long.41:16
Foul by David Hunt on Jamie Murphy, free kick awarded. Free kick crossed right-footed by Ryan Flynn, Mat Sadler makes a clearance.41:04
Free kick awarded for an unfair challenge on Harry Maguire by Jamie Proctor. Free kick taken by Harry Maguire.40:39
The ball is delivered by Billy Clarke, clearance made by Matthew Hill.40:05
Ryan Flynn has an effort at goal from outside the penalty box that bounces off the post.39:44
A cross is delivered by Billy Clarke, Matthew Hill gets a block in.39:11
A cross is delivered by Ryan Flynn, save by Paul Jones.38:45
Outswinging corner taken right-footed by Ryan Flynn from the right by-line.38:36
Matthew Hill crosses the ball, blocked by Dannie Bulman.36:42
Long distance shot from Billy Clarke misses to the left of the target.35:16
Joe Walsh gives away a free kick for an unfair challenge on Dave Kitson. Direct free kick taken by Ryan Flynn.34:56
Nicky Adams sends in a cross, George Long makes a save.33:38
Dannie Bulman produces a left-footed shot from just outside the penalty box that misses to the left of the target.32:29
Nicky Adams decides to take a short corner.32:20
Mat Sadler produces a cross, blocked by Ryan Flynn.30:45
Jamie Proctor concedes a free kick for a foul on Matthew Hill. Strike comes in from Danny Higginbotham from the free kick, save made by Paul Jones.30:09
Jonathan Forte crosses the ball.28:50
Free kick awarded for a foul by Jamie Murphy on Nicky Adams. Direct free kick taken by Mat Sadler, Billy Clarke sends in a cross, save made by George Long.27:57
Effort from long range by Kevin McDonald goes wide right of the target.27:46
Centre by Dave Kitson, Joe Walsh makes a clearance.25:51
Nicky Adams sends in a cross, save by George Long.23:42
Billy Clarke has an effort at goal from outside the penalty box which goes wide left of the goal.23:26
The ball is crossed by Jonathan Forte, clearance made by Dannie Bulman.21:59
Corner from the right by-line taken by Ryan Flynn, Neill Collins produces a header from inside the area that goes over the crossbar.21:49
The ball is swung over by Ryan Flynn, blocked by David Hunt.20:25
The ball is crossed by Mat Sadler.18:58
The ball is crossed by Matthew Hill.15:54
Corner taken right-footed by Ryan Flynn, clearance made by Dannie Bulman.14:23
The referee blows for offside. Paul Jones takes the indirect free kick.13:09
Free kick awarded for a foul by Michael Doyle on Dannie Bulman. Dannie Bulman takes the direct free kick.12:47
Billy Clarke produces a cross, clearance by Matthew Hill.12:22
The ball is swung over by Nicky Adams.10:13
Jonathan Forte sends in a cross, clearance made by Mat Sadler.8:38
Jamie Murphy delivers the ball, clearance made by Mat Sadler.8:20
Centre by Ryan Flynn, David Hunt makes a clearance.7:28
A cross is delivered by Nicky Adams, save by George Long.6:48
Jamie Proctor gives away a free kick for an unfair challenge on Danny Higginbotham. Neill Collins restarts play with the free kick.3:04
Dannie Bulman sends in a cross, Matthew Hill makes a clearance.2:10
The referee blows for offside. George Long restarts play with the free kick.0:25
Free kick awarded for an unfair challenge on Michael Doyle by Nicky Adams. Free kick crossed by Ryan Flynn, Sergio Torres manages to make a clearance.0:00
The referee starts the match.
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