Oldham Athletic rattled up their fifth victory on the trot to continue their excellent start to the season in Nationwide Division Two.
But they had substitute Wayne Andrew to thank for claiming all three points at out of sorts Colchester.
Andrews, who was introduced as a substitute in the 62nd minute, struck what proved to be the winner just two minutes later.
Andrews had his back to goal on the edge of the penalty area before turning to unleash an unstoppable left-foot drive which took a slight deflecting off Kemal Izzett on its way into the top corner of the net.
Both sides had been reduced to ten men earlier in the second half in a bad-tempered affair.
Oldham skipper Clint Hill was shown the red card for serious foul play on 53 minutes when he lunged at Colchester front runner Mick Stockwell.
In the melee that followed, Colchester skipper Mark Warren was also sent off for what the fourth official deemed to be violent conduct.
The U's will be appealing against that decision after watching the incident on video.
Both sides had to play with just ten men, and it was high-flying Oldham who came out on top although Colchester had an excellent chance to score in the 81st minute.
Stockwell squared into the path of Dean Morgan and he had just keeper Les Pogliacomi to beat. Yet the Oldham keeper rushed off his line and made a vital block to protect Oldham's slender lead.
The hosts also had one excellent chance to score in the first half when Stockwell missed from just five yards out with a header following a good nod-on from team mate Scott McGleish.
This was Colchester's fourth straight defeat, and they are beginning to slip down the table after a satisfactory start.
Colchester manager Steve Whitton said: "I am bemused and disappointed by the fourth official's decision to send off Mark Warren.
"Once again missed chances cost us. We have got to do better in these attacking situations."
Oldham manager Iain Dowie added: "We were not at our best attacking wise, but it's great to keep our run of victories going."