Jevani Brown scored a late consolation goal as Peterborough win the first game of the evening.
Two goals from Dan Butler and one from Sikiri Dembele ensure the Posh win the game.
The visitors were two up at the break, before Butler scored his second of the game seven minutes after the break.
Jevani Brown finished off a fine move to find the net for the U's.
STARTING XI: Gerken, Bramall, Smith, Pell, Brown, Harriott, Chilvers, Scarlett, Eastman, Stevenson, Gambin.
The opening exchanges of the game were tight, with the visitors just edging the best of the chances.
Sikiri Dembele looked dangerous as he pushed forwards and should really have put the Posh in front after quarter of an hour played. He lifted his header just over the bar with little pressure.
Dembele forced Dean Gerken into his first save of the game a couple of minutes later. The visiting forward cut in and shot straight down the throat of the U’s keeper, with Gerken able to beat the ball away to safety.
Gerken was again called into five minutes later when he scrambled across to push away Jake Taylor’s free kick.
Callum Harriott was the first U’s player to get a shot away towards goal. He cut inside from the right flank and lifted a shot towards the far top corner, but got too much lift on the ball as Christy Pym was able to watch the ball comfortably over the bar.
On the half hour mark, the U’s found themselves a goal down. Reece Brown raced towards goal before sliding the ball over to the onrushing Butler who was able to get his shot on goal. The ball was going in anyway, but Harry Pell steered the ball into his own net in desperation.
Peterborough United doubled their lead three minutes later, through Sikiri Dembele. His solo run allowed him the space to fire the ball into the top corner of the net beyond Dean Gerken.
The visitors had another chance just before the break when Mohamed Eisa struck a free kick that was just tipped over the bar by Dean Gerken before the half time whistle was blown.
Seven minutes into the second period the Posh added a third goal for the evening. Dembele slid the ball down the wing to Butler who rifled the ball into the roof of the net giving Gerken no chance.
With ten minutes to go, the U's found the net with a fantastic move finished off by Jevani Brown.
Luke Gambin laid the ball back to Miquel Scarlett who drove at the Peterborough defence before picking out an inch perfect pass for Brown to sweep the ball beyond Pym and into the back of the net.
Colchester United were pressing for a second late on, but struggled to break through a strong visiting defence.