Colchester needed a dramatic late goal against National League side Altrincham to win 3-2 at the Weston Homes Community Stadium and progress through to the Third Round.
In a cup famous for upsets, the U's had to come from behind twice as goals from Altrincham's Jake Moult and Michael Rankine were cancelled out by two goals from Callum Harriott either side of a Tom Lapslie header.
The first half began in dramatic fashion as after just three minutes Altrincham's Moult produced a moment of FA Cup magic as he spectacularly chipped Jamie Jones from 30 yards to give the visitors the lead.
Colchester responded well from the early shock and had two quick chances through Harriott and George Moncur. Harriott had a good shot saved before Moncur pulled a shot just wide.
Altrincham had a great chance to double their lead from the resulting goal kick as the ball found its way through to Damian Reeves and Jones was almost caught out again as Reeves tried a lob. This time it fell on the roof of the net to the relief of the U's keeper.
Jones was called into action again shortly after as the visitors really were playing well but it was a mistake that allowed Colchester to get back in the game.
The Altrincham defence failed to clear their lines and instead gifted the ball to Harriott. He played a neat one-two with Marvin Sordell and coolly slotted the ball under the onrushing goalkeeper.
Following the equaliser, Colchester began to look increasingly more dangerous as the half progressed and Harriott almost grabbed he combined well with Moncur before firing just over.
Despite Colchester looking more fluent going forward there were two half chances for Altrincham before half time but Jones was there to parry away Jordan Sinnott's free kick and Scott Leather was unable to direct a header from a corner.
The second half began in more dramatic fashion that the first as Altrincham were lightning quick out of the blocks to retake the lead.
A long ball from the back straight from kick off fell to James Lawrie's feet and he played a good ball round the corner to set up Rankine who did the rest.
Colchester once again responded well from going behind and created several chances that fell to Lapslie but he was unable to convert. First, he had a headed over from outside the six yard box following a Gavin Massey cross.
Then Harriott's trickery meant he could pick out Lapslie but his shot was blocked from close range when he looked certain to score.
Lapslie didn't have to wait too long for his next chance to come around and this time he made no mistake.
On 53 minutes Sordell was played in by Harriott down the left hand side of the box and he produced a chipped cross that Lapslie headed home to make it 2-2.
Just when it looked like momentum had swung In favour of the U's again, Altrincham nearly went ahead for a third time but Rankine Somehow volleyed over from inside the box.
As the game reached the final ten minutes, Colchester had two more chances in quick succession but Tim Deasy made two good saves to deny Moncur and full back Matt Briggs.
As the tie looked to be heading to a replay, four minutes was added on and what a dramatic four it was. Harriott had a powerful header tipped over by Deasy and Altrincham had a great chance to win it as they countered the result corner.
Sub Nicky Clee broke clear down the left hand side and turned Briggs but his shot was saved by Jones to the disbelief of the Altrincham fans and management team.
This disbelief turned to heartbreak in the final few moment as a lose header fell to Harriott and he lashed the ball into the top corner of the net to deny the visitors a deserved replay.
The U's will now face Charlton on the weekend of the 9th January.