Colchester secured a vital victory over fellow strugglers Leyton Orient but remain two points from safety at the foot of League One.
Gavin Massey opened the scoring for the hosts as he swept home from close in.
Kaspars Gorkss’ header doubled the lead before Chris Dagnall thought he had pulled one back for Orient, only for his effort to be ruled out for offside.
The hosts’ win was soured when Elliott Hewitt was shown a straight red card for a foul on Romain Vincelot.
The U’s leapfrog Orient as a result of the win but both teams remain in the League One relegation zone.
Leyton Orient manager Fabio Liverani told BBC London 94.9:
“We have to fight until 2 May, the last game to avoid relegation because this is what we can fight for. Last season was great, but it has past so this season it is a strong battle to avoid relegation.
“We knew that Colchester would push a lot in the first 20 minutes and we prepared for the game in that way but then on the pitch it was a different story.
“They showed more desire and hunger than us and this is what I said to the players – we have to play with that sort of spirit to go ahead and progress in the league.”