Sammie Szmodics proved to be the hero of the day again, earning the U’s an away draw in the fifth minute of stoppage time.
Mansfield substitute Craig Davies was on course to grab all three points for the Stags when he put them in front at the second attempt from 18 yards, nine minutes from time.
But a long throw from Ryan Jackson was met by a slight touch from Szmodics and the ball went through the hands of goalkeeper Conrad Logan.
The visitors had defended strongly against a Mansfield side that had scored 11 goals in their previous three games.
There was little action to report in the first half, with the U’s producing the only real chance in the 18th minute.
From their first corner, Colchester tested keeper Logan as Brennan Dickenson floated the ball to the far post where Luke Prosser’s strong header was turned away.
Next up for the U’s: Crewe Alexandra at the Jobserve Stadium on Tuesday 21st August.