Match ends, Colchester United 0, Sheffield United 1.
Sheffield United secured a sixth straight win as Chris Porter's second-half penalty saw off Colchester United.
Freddie Sears clipped Ben Davies in the box and Porter netted his eighth goal of the season with three minutes to go.
The visitors dominated the game but rarely troubled Sam Walker, although the Chelsea loanee had to be at his best to deny a Ben Davies volley.
Colchester's best chance of the game fell to Sears but he saw his flick drop just wide of the post.
The Blades are now six points clear of the League One relegation zone, while Colchester remain only three points away from the bottom four.
Jose Baxter had the game's first chance as he went close for the visitors, while Jamie Murphy cut inside and fired wide.
A well-worked move resulted in Conor Coady, who was celebrating his 21st birthday by agreeing a loan extension from Liverpool until the end of the season, having a shot deflected wide.
John Brayford's header was easily saved by Walker, while Baxter also went close in the second half.
United's winner came when Davies, on loan from manager Nigel Clough's former club Derby County, jinked his way into the box.
Second-half substitute Porter, who came off the bench to score from the spot against Nottingham Forest in the FA Cup, repeated the trick to secure his side three points.
Colchester United manager Joe Dunne told BBC Essex:
"It would have been unjust to Sheffield United [for us] to have got a point, but I would have taken it based on how poor we were in the first half.
"Aimless balls from back to front kind of nullified what we were asking the players to do, that was the disappointing part.
"We could have been there till Christmas and probably not scored. We were just off our game tonight.
"They are working hard and when it goes tough, you've got to stick with them. My players will respond."
- 20WilsonSubstituted forSesayat 46'minutes
- 3DicksonBooked at 40mins
- 18EastmanBooked at 90mins
- 9MorrisonSubstituted forEastmondat 46'minutes
- 22DaviesSubstituted forHillat 89'minutes
- 8DoyleBooked at 41mins
- 11BaxterSubstituted forPorterat 83'minutes
- 23MurphySubstituted forFlynnat 81'minutes
- Graham Scott
- Shots on Target
Second Half ends, Colchester United 0, Sheffield United 1.
Foul by Craig Eastmond (Colchester United).
Ryan Flynn (Sheffield United) wins a free kick in the defensive half.
Attempt missed. Jabo Ibehre (Colchester United) header from the centre of the box misses to the right.
Alie Sesay (Colchester United) wins a free kick in the attacking half.
Foul by Stefan Scougall (Sheffield United).
Tom Eastman (Colchester United) is shown the yellow card.
Substitution, Sheffield United. Matthew Hill replaces Ben Davies.
Goal! Colchester United 0, Sheffield United 1. Chris Porter (Sheffield United) converts the penalty with a right footed shot to the bottom left corner.
Penalty conceded by Freddie Sears (Colchester United) after a foul in the penalty area.
Penalty Sheffield United. Ben Davies draws a foul in the penalty area.
Substitution, Sheffield United. Chris Porter replaces Jose Baxter.
Attempt missed. Michael Doyle (Sheffield United) left footed shot from outside the box is high and wide to the left.
Attempt saved. Jose Baxter (Sheffield United) right footed shot from outside the box is saved in the centre of the goal.
Substitution, Sheffield United. Ryan Flynn replaces Jamie Murphy.
Attempt missed. Magnus Okuonghae (Colchester United) header from the centre of the box misses to the left following a corner.
Corner, Colchester United. Conceded by Harry Maguire.
Attempt missed. Jose Baxter (Sheffield United) right footed shot from outside the box misses to the right.
Attempt missed. Neill Collins (Sheffield United) right footed shot from the centre of the box is too high following a corner.