An Andy Taylor equaliser six minutes into stoppage time earned Walsall a deserved point at Colchester.
The left-back fired home a free-kick with virtually the last kick of a game the Saddlers largely dominated.
Freddie Sears had put the hosts ahead after just seven minutes when he lashed home a shot from the edge of the box after being left unmarked.
But James Baxendale and Sam Mantom both hit the woodwork for the visitors, who forced an incredible 15 corners during the game.
Dean Smith must have thought the equaliser would never come but it was not more than his side deserved.
With Milan Lalkovic away on international duty, Smith introduced Baxendale to the starting line-up while there was also a place for Ashley Hemmings as Troy Hewitt dropped to the bench.
The Saddlers made a bright start and Baxendale tested home keeper Sam Walker early with a shot from the edge of the box, following a lovely passing move. Craig Westcarr then pulled a shot just wide of the near post after being played in by Mantom.
But the hosts went ahead in the seventh minute from their first real attack. Marcus Bean found an unmarked Sears on the edge of the box, who made the most of the time and space available to him by lashing a shot past O’Donnell and into the corner.
Westcarr struck a free-kick straight at Walker as the Saddlers looked for a quick leveller, while at the other end Luke Garbutt curled a free-kick just the wrong side of the near post. Garbutt was looking bright and had appeals for a penalty waved away after going down following a mazy run into the box.
The Saddlers had lost their fluency of the early stages and a poor touch by Paul Downing allowed Jabo IBehre clear but the former Walsall man pulled his shot wide of the post.
That miss seemed to spark the visitors and Baxendale almost levelled with a snapshot from the edge of the box which cannoned off the crossbar and was cleared behind. From the resulting corner, Butler was adamant his goalbound header had been blocked by a hand but the referee again waved away the appeals.
Butler sent another header straight at Walker, while Mantom had a shot blocked as the visitors upped the pressure.
But the hosts still looked dangerous and Gilbey whipped a ball across the face of the visiting six yard box, while Ibehre headed a Matt Taylor cross wide.
Ibehre also fired in a right-footed effort which was easily gathered by O’Donnell, before Mantom came within inches of tying things up in first half stoppage time but saw his shot with the outside of his foot from 25 yards out strike the post.
Hemmings had the first shot of the second period but his low drive was easily gathered by Walker. The home keeper also comfortably dealt with an Adam Chambers header from a Westcarr cross, while Hemmings had a fierce shot blocked as the Saddlers continued to probe without any fortune.
Despite their substantial possession, Walker was remaining largely untroubled and Smith introduced Romaine Sawyers and Julian Gray with 20 minutes remaining.
Adam Chambers failed to take advantage of the time and space when he was found by a Hemmings free-kick and headed hurriedly over.
Home substitute Jeffrey Monokana had a shot blocked by Andy Taylor as the hosts looked to put the result beyond doubt, while Sawyers saw two efforts charged down at the other end.
Hemmings drove a fierce shot over from around 25 yards out before he was taken off for Hewitt in the final ten minutes.
But chances were still at a premium despite the pressure. James Chambers headed wide from a corner while Butler sent one straight at Walker as the game entered stoppage time.
Gray shot over from eight yards out as the clock ticked down before Taylor’s last-gasp heroics. The visitors were awarded a free-kick 25 yards out and Taylor curled home to earn the point.
Walsall FC boss Dean Smith spoke after his side clinched a late equaliser: " It was a fantastic free-kick by Andy Taylor, hit right into the top corner.
"We deserved a point. The team were terrific and displayed some good football. We hit the bar, the past and troubled the keeper.
"The lads didn't give up. We did everything right and kept creating chances. When Andy scored his free-kick we wanted to go on to push for a winner, it's a great mentality that lads have got.
"Romaine Sawyers is a clever player. he plays well in the 4-4-1-1 just off the striker. When you bring someone like him on in the 65th minute, he will expose the tired opposition and he did that today.
"I believed we would get something from today, slightly disappointed it was a draw but a superb free-kick from Andy Taylor gave us a well deserved point."