Three second half goals from the visitors turned the game on its head as the U's first home friendly ended in defeat to Charlton Athletic.
It all looked promising for the home side when the U's found themselves two goals to the good courtesy of Freddie Sears superb strike and Tommy Smith's powerful header after forty minutes.
But Charlton struck the next four goals in the contest, with Gilbey, Leaburn and Morgan all on target combined with Alan Judge's own goal to give the visitors the win.
The visitors started the game on the front foot and after hitting Dartford for six in their previous game, looked to get ahead early against the U's. Seeing an early effort cleared off the line from Ryan Clampin, Colchester soon settled their nerves and were back in their stride in the opening fifteen minutes.
And Wayne Brown's side soon had a golden chance of their own to open the scoring. Emyr Huws was putting the pressure on the Addicks defence, as they attempted to play the ball across their back four, but the stray pass fell kindly for Frank Nouble. It looked for all the world that he would score with all-but an open goal in front of him, but he lifted the ball against the bar and out of the danger-zone for a goal kick.
But the U's did get their noses in front twenty minutes later when Freddie Sears struck his first of the summer, with a sumptuous strike. Turning quickly from around thirty-yards out, Sears struck an unstoppable effort over MacGillivray and into the back of the net.
One quickly became two, this time with Tommy Smith getting his name on the scoresheet against the Addicks. Grappling with his man at the back post, the U's captain got the better of his counterpart to head the ball powerfully back across goal and into the back of the net despite a touch from the 'keeper on the way through.
Almost as speedily as the U's had doubled their advantage though, it had been halved when former U's midfielder struck for his side. Striding through the middle, Gilbey was able to shrug off the challenge of Tommy Smith before coolly stroking the ball under Shamal George.
The half time whistle would come moments later, with the U's holding a slight advantage over their opponents, as Emyr Huws was withdrawn for Triallist for the second period.
Shortly after the second half had kicked off, the visitors were back level in the game, with Alan Judge putting the ball into his own net. A fiendish cross was delivered from the right flank for the Addicks, with the U's midfielder almost given no choice but to get contact on the ball, unfortunately tapping in from inside the six-yard area.
Ben Garner's side managed to get themselves in front for the first time in the game twenty minutes into the second period, with Miles Leaburn hitting the target. He was able to calmly control the ball before rounding Hornby and passing the ball into the empty net to make it 3-2.
It quickly became four, with Albie Morgan adding to Charlton's tally five minutes later. A quick one-two beat the U's defence, with Morgan able to smash the ball into the top corner beyond Sam Hornby, putting the game beyond doubt for the visiting side.
The full time whistle blew at 4-2 to Charlton Athletic, although it was an encouraging performance from the U's who are back at the JobServe Community Stadium again on Friday evening, when Millwall visit North Essex.
Colchester United starting XI: George, Coxe, Chambers, Smith, Clampin, Skuse, Judge, Huws (Triallist), Hannant, Sears, Nouble.
Last Thirty Minutes: Hornby, Tchamadeu, Eastman, Terry, Kazeem, Triallist, Marshall Miranda, Cooper, Chilvers, Sayer, Akinde.
Unused: Beadle, Hutchinson.