Former Bristol City player Kayode Odejayi pushed Bristol Rovers deeper into the relegation mire as his first-half strike gave Colchester a 1-0 win.
In the 22nd minute an attempted clearance from goalkeeper Conrad Logan rebounded off the back of defender Jerel Ifil and into the path of Odejayi, who ran through unchallenged to score.
It was no more than Colchester deserved as Jean-Paul Kalala twice saved Rovers with goal-line clearances, while Logan made good saves to deny Odejayi on two occasions.
Jo Kuffour fired narrowly over on 52 minutes following a good run by Chris Lines, but it was a rare moment of anxiety for visiting goalkeeper Ben Williams.
Former Rovers' boss John Ward was able to celebrate a winning return to the Memorial Stadium, while current manager Dave Penney looks to be facing a huge task to keep the Pirates in League One.