Posh led 1-0 at the break thanks to a Jonson Clarke-Harris goal, but lost their way in the second perios and let the hosts back in with a penalty after a goalkeeping mistake and a bit of dozy defending.
Mostly, one eleven played for around 55 minutes until Darren Ferguson withdrew them early in favour of a second originally scheduled to play the final 30.
Nicholas Bilokapic and Peter Kioso appeared in Posh colours for the first time.
The players are listed below in the order of the side that began the game followed by the one that ended it.
13. WILL BLACKMORE (on 45 mins)
Should get credit for a flying save he made to keep the score at 1-1 but there is no escaping the moment where he spilled a cross then proceeded to produce a weak throw right to Crichlow, who wasn't expecting the pass and conceded a penalty. 5. Photo: Joe Dent
14. HARRISON BURROWS (on 55 mins)
Made little impact on the game at left-back. Posh were being exploited down the wings in the second half but it was mostly on the opposite side. 6. Photo: David Lowndes
15. ROMONEY CRICHLOW (on 55 mins)
Has to carry the can along with Blackmore even if the keeper is more at fault but he was out muscled and did bring his man down. Made a telling contribution at the end though to slide in and stop John Akinde winning in with a counter-attack. 5.5 Photo: Joe Dent
16. CHARLIE O'CONNELL (on 55 mins)
The physicality of the match looked a bit much as Colchester got on top and it rather passed him by. 6. Photo: Joe Dent