Former United hero, Jamie Cureton, netted a hat-trick, sandwiched between goals from Jon Otsemobor and Dion Dublin.
Kevin Lisbie scored for the U's, but this was a day for the home fans to celebrate from start to finish.
The visitors kicked off attacking the River End goal and had the first shot with Johnnie Jackson firing over.
However, they were behind in the sixth minute when Otsemobor burst into the penalty area to beat Dean Gerken high to his left with a firm right-foot shot from 12 yards.
Ten minutes later Jackson had another shooting opportunity but fired wide.
Good play by Ryan Bertrand set up Darel Russell, but at full stretch his shot went into the sidenetting.
Gerken pounced on the ball to deny Darren Huckerby a shooting chance, while at the other end Kemal Izzet brought a save from David Marshall with a long-range shot.
Ten minutes before half-time Huckerby crossed from the right and Cureton beat Gerken at the near post with firm right-foot volley.
Lisbie's header bounced over via the top of the crossbar, but seconds later John White's throughball fell to him from Jason Shackell's header and he calmly took the ball round Marshall and rolled the ball into the net with his left foot.
Colchester forced a string of corners at the end of the first half without making any of them count.
Gerken saved a shot from Bertrand early in the second half, then Huckerby crossed from the right, but Dublin opted to head down rather than going for goal and the ball was cleared.
Dublin then lobbed Gerken only to see the ball come back off the bar.
Eight minutes into the second half Phil Ifil tripped Matt Pattison on the six-yard line and Cureton converted the resulting spot-kick, sending Gerken the wrong way with a right-foot shot to his left.
Cureton's treble was completed on 87 minutes when Dublin laid off Maceo Rigters' cross and Cureton passed the ball into the net with a right-foot shot from ten yards to the keeper's left.
Dublin made if five in stoppage time, collecting Russell's pass on the edge of the box and calmly finding the top right-hand corner with a right-foot chip.