John-Joe O'Toole scored four minutes into stoppage time to clinch Colchester's entry into the Third Round of the FA Cup as they squeezed past Hereford 1-0.
Substitute Anthony Wordsworth cut the ball back to O'Toole who drove it past goalkeeper Adam Bartlett from 12 yards.
It was a bitter blow for Hereford who had been the better side in the first half.
The Bulls were the first on the offensive with striker Gavin McCallum clipping the Colchester cross bar with a shot from the left flank.
Teenager Jordan Mutch, who joined Hereford on loan from Birmingham City on Thursday, also volleyed over the cross bar from a cross by Craig King
Colchester however hit back with Steven Gillespie having a low drive parried away by Bartlett.
Hereford full back Ryan Green a cleared an on-target header from Kayode Odejayi off the line.
But Hereford hit back with Darren Jones drilling a long range shot on target but Colchester keeper Williams made a fine save to tip the ball over the cross bar.
After the break play continued to switch from end to end but nothing was settled until stoppage time when O'Toole snatched the winner.
