Colchester eased through to the second round at the expense of troubled Mansfield in a first round replay at Layer Road.
Nothing went right for Mansfield in what was a very one-sided match.
Missing several players through injury and suspension - and with Carlton Palmer in charge on a temporary basis due to the suspension of Keith Curle pending an internal enquiry - matters went from bad to worse for them at Colchester.
The Essex hosts took the lead after only 10 minutes when Australian born midfielder Richard Garcia headed home John White's cross for his third goal of the season.
Three minutes later and it was 2-0 to the Us. Sam Stockley swung over a cross and Mansfield midfielder Tom Curtis could only divert the ball past Kevin Pilkington for an own goal.
The Stags suffered a further setback early in the second half when Adam Murray was stretchered off with what looked like a serious leg injury following a strong challenge by White.
Mansfield's misery deepened when defender Alex Baptiste was sent off in the 68th minute after he had given away a penalty.
The assistant referee spotted a push on Craig Fagan and when the Mansfield defender started to complain, referee Keith Hill also showed him a red card.
Up stepped Colchester striker Fagan to convert the penalty, so rattling up his seventh goal of the season, although it was his first in two months.
The visitors pulled a goal back in the 86th minute thanks to a clinical shot from Alex Neil.
There was still time for Colchester to add a fourth goal.
Garcia was pushed in the box by Mansfield defender Luke Dimech and substitute Gareth Williams swept home the ensuing penalty to wrap up a comprehensive victory in the fifth and final minute of injury time.