An action packed match ends all square.
Despite having the better of the chances, they found themselves two down at the break to a Walsall side that had only conceded two in their previous seven away games this season.
Yet within five minutes of the restart, the U's were level - but that was only the beginning of a quite amazing second forty-five minutes.
Having dragged themselves back to 2-2, the U's quickly fell behind, before Owen Garvan scored a goal of the season contender to make it 3-3.
Darren Ambrose got the U's in front for the first time with a move he started and finished to cap his best game in a Colchester shirt before, deep in injury time, the Saddlers showed their mettle by grabbing a late equaliser.
The game started at a frenetic pace, which gave some indication of what was to come.
First Sordell lifted the ball over from close range, before Morris was denied for the Saddlers.
But the visitors did go in front after just ten minutes. Romaine Sawyers found space in the box and crashed home a fine effort to put the Saddlers a goal to the good.
The U's were probably having the better chances through the first forty-five minutes but fell further on the half hour mark when Milan Lalkovic's long range shot clipped Tom Eastman and nestled in the bottom corner of the net.
Tony Humes was probably left wondering on the sidelines how his side were two behind, but they knew that they had done enough to test their opponents' defensive resolve.
And they came flying out of the blocks at the start of the second period.
First Garvan fed the ball into the path of Moncur, who curled a sumptuous effort right into the top corner to give the U's hope.
That hope turned to expectation three minutes later as Sordell tucked home from close range from an Ambrose cross after another fine pass from Garvan.
The U's had their tails up and looked like they might then take the lead, only for the visitors to get back in front as the ball came to Evans twelve yards out to smash home his second goal for the Saddlers.
The home side were not to be cowed, though. The ball fell to the impressive Garvan 25 yards or so from goal and he hit a sublime first time, half volley that cruised through the air to rustle the far side netting at 3-3.
Then, with 15 minutes to go, they were in front for the first time. Ambrose started and finished a move that ended with him sidefooting home from the same spot that Garvan had got his goal.
At 4-3, the Weston Homes Community Stadium was bouncing and the U's looked like they might be on their way to a memorable victory.
And yet there was one more twist on an afternoon full of incident.
The ball was fed into the penalty area deep into injury time and central defender O'Connor tucked home to break U's hearts.
The visitors even crashed a shot against the upright after that, but there had been enough drama for one day and both teams left the pitch to warm applause on a memorable day at the Weston Homes.