TONY HUMES' first home game in charge ended in an agonising 3-2 defeat to Sheffield United.
The U's were two goals up with 13 minutes left but conceded three goals in a crazy five minute spell late on.
George Moncur's first half strike gave the U's a deserved lead at half time as his powerful rebounded headed gave the U's the lead on the half hour.
Freddie Sears doubled the U's lead in the second half when he pounced on a goalkeeping error by Mark Howard and the U's seemed to be cruising to vistory.
But the Blades scored three goals in five minutes to complete a dramatic turnaround in the final ten minutes.
Ben Davies scored the first with a driven shot across the face of goal. Ryan Flynn then levelled it with a close range finish two minutes later.
And the turnaround was complete when Nigel Clough's side were handed a penalty following Alex Gilbey's foul. Davis stepped up and calmly slotted the ball past Sam Walker.
Tony Humes was forced into making one change for his first game in charge. Captain Magnus Okuonghae, who was sent off in the 2-0 victory at Leyton Orient, was replaced by Frankie Kent, who was handed his home debut.
Humes' first home game almost got off to a flyer when Moncur offloaded a fizzing shot that ended narrowly wide of the left-hand upright.
The U's then came the width of a post from taking the lead when the ball dropped to Gilbey in the box but his thumping volley rebounded clear off the post with Howard rooted in the Blades goal.
The visitors then had a chance of their own when Robert Harris sent a speculative effort at goal but his attempt ended well wide of the target.
Colchester then looked to get on the front foot again and Freddie Sears deflected shot from just outside the box had Howard scrambling across his goal to put the ball bahind.
The U's then got the goal that their play deserved through Moncur. After a flowing move Sears got to the byline and pulled the ball back to Moncur who struck his shot first time and pulled a superb reaction save from Howard.
But the Blades keeper was helpless to prevent Moncur powering in the rebound from a header to give Humes' side a lead they carried into the break.
The visitors came flying out the blocks second half and James Wallace had a half chance within two minutes of the restart when his close-range shot hit the side netting with Walker rooted.
The U's then had a golden chance to double their lead when Sears latched onto a through ball and rounded Howard but with the goal at his mercy the former West Ham striker's shot was miraculously cleared off the line by Neill Collins.
Sears had another chance to atone for his earlier error when he beat a defender and fired in a shot that fizzed just past the right-hand upright.
But he did eventually got his goal and it came from a huge blunder by Howard in the Blades net. The keeper slid out to collect a routine back header but spilled the ball to Sears who calmly curled his shot into an empty net.
The Blades pulled one back six minutes later through Davies' drilled effort across the box to set up a nervy finish.
And they levelled it two minutes later when Mark McNulty's pull back was crashed in from close range by substitute Flynn.
Davies finished off the Blades' rally following Gilbey's foul on Stefan Scougall, the midfielder calmly sending Walker the wrong way to seal the victory.
The U's now lie 22nd in the table and host former manager Phil Parkinson's Bradford City on Saturday.