Ian Henderson came off the bench to score a late winner as Colchester dented Rochdale's play-off hopes with a 1-0 victory.
Henderson planted a shot past Owain Fon Williams and into the net from close range with four minutes to go, despite Craig Dawson's desperate attempts to keep it out.
Rochdale striker Chris O'Grady headed Nicky Adams' cross just wide in the first half and then forced Colchester goalkeeper Ben Williams to turn his first-time effort around the post.
Colchester's best effort of the first half came when Ashley Vincent's deflected first-time shot from the edge of the area flew just wide.
Rochdale went close again just before the hour mark when Matt Done blasted wide from a good position from Will Atkinson's cross.
Williams denied O'Grady at his near post before Henderson finally broke the deadlock. And although Dale substitute Jean Louis Akpa Akpro rattled the crossbar late on and Nathan Clarke headed Joe Thompson's effort onto the woodwork, Colchester held out.