A good U's performance is left unrewarded.
Two down at the break, the U's looked like they might claw Peterborough back with a spirited and determined display, but were undone by a late third for the visitors.
The U's were left to rue another defeat on Saturday afternoon in a performance that merited more.
Following a miss from the penalty spot Conor Washington redeemed himself giving Posh the lead midway through the half, not long after Kgose Nthle doubled from close range.
Colchester had been unlucky to be two down and after the break their positivity was rewarded with a goal from Freddie Sears who looked to start a comeback thanks to great play from Sanchez Watt.
As U’s pushed and pushed for the equaliser, Peterborough punished them on the break, securing the win via Jermaine Anderson’s strike. Nthle saw red late on but made this no difference to the result.
It was drama from the first minute as Sammie Szmodics was deemed to have handled a Peterborough free kick from inside the box, gifting Posh an early penalty.
Washington stepped up for the spot kick but his low effort was matched by Sam Walker, diving down to his right to keep out the penalty before Magus Okounghae cleared the ball.
At the other end Jabo Ibehre and Freddie Sears were lively and pressured Christian Burgess into a mistake, with Sears stealing possession before breaking away down the right flank.
With Ibehre ready for the pull back, Sears instead opted for a cross looking to pick out Gavin Massey at the far post. Ricardo Santos slipped at the vital moment allowing Massey to get his shot away.
Ben Alnwick reacted quickly to block the low shot from Massey and as the loose ball rebounded to Ben Gordon, Alnwick was ready again to keep out a second powerful near post shot.
The failure to take chances again cost Colchester dearly as Posh made a breakthrough. Burgess under pressure made up for his previous mistake with a clever reverse pass from his own half, Washington ran onto it and slotted calmly past the on rushing Sam Walker.
With decisions going against U’s bad turned to worse as Peterborough scored again. An inviting ball swung deep across the box was met by Kgosi Ntlhe at the far post and he finished, doubling the lead.
As Colchester look to right their wrongs Sears forced a fine save from Alnwick with a dipping shot from outside of the box, Ibehre met the resulting corner but flicked frustratingly over the bar.
A lengthy stoppage in play was required as Shaun Risley eventually had to come off early, being replaced by Gabriel Zakuani after colliding with a team mate.
Walker was forced into an acrobatic save late on as Posh top scorer Kyle Vassell headed the ball just under the cross bar.
An addition of six minutes of injury time provided no more drama in the first half with Posh going in two up and top of the league.
Chances continued to come early in the second half, first for Peterborough as Vassell turned Eastman in the box and got a shot away, only to be denied by the legs of Walker.
In the opposing half Szmodics and Alex Gilbey were combining well for U’s before the latter lashed a shot onto the underside of the bar, luckily for Posh the bounce took the ball back away from goal.
Joe Dunne wasted no time in making a double change for Colchester as Szmodics and Gavin Massey made way for Dominic Vose and Sanchez Watt.
The latter made an instant impact on the left hand side as his direct play teed up Sears for a first time shot inside the box, the shot however summed of U’s afternoon so far as it glanced wide.
But this was a momentary respite for Peterborough as U’s pulled a goal back. It was that same combination of Watt and Sears, this time with a finish that neither Alnwick nor the post could keep out.
The goal brought Colchester a new lease of life with Watt continuing to cause problems out wide. A big handball shout against Zakuani was dismissed by the referee to the amazement of U’s players.
The frustration grew as against the run of play Peterborough grabbed a third. A dangerous ball found its way across goal and into the path of Jermaine Anderson who side footed it home.
But the game wasn’t finished there as Posh handed U’s a lifeline back into the game, curtesy of gaol scorer Ntlhe’s second yellow card which sent him for an early bath.
Colchester upped the pressure with Sears orchestrating play through the centre but as all ten men got behind the ball the Posh defence was even harder to break down.