Colchester grabbed a seventh straight home league win as Southend ended the game with nine men in a lively derby. Southend captain Kevin Maher and Mark Gower were sent off early in the second half and the U's were soon ahead.
Greg Halford netted with a 68th-minute shot and soon after Pat Baldwin scored when the ball came back off the bar.
Colchester were reduced to 10 men when Chris Barker was shown a second yellow card, but Jamie Cureton's close-range finish on 85 minutes extended the lead.
606 DEBATE: Give your thoughts on the match
Colchester manager Geraint Williams, speaking on Kevin Maher's accusation that Karl Duguid was responsible for his dismissal, a claim Duguid denies:
"I was watching the flight of the ball and I looked back and saw Maher picking
Duguid up.
"I can't condone anyone getting someone sent off. If something has happened I'll take internal action. But I don't think anyone got anyone sent off. The ref
has had reasons to send people off.
"It's another three points for us from an Essex derby and we're very pleased."
Southend manager Steve Tilson, speaking about Maher's red card, against which he is going to appeal:
"When it was 11 v 11 we were comfortable. It didn't feel like a normal derby with bad tackles until then.
"Kevin said he didn't touch him but he's gone down. I can't fault the players for their effort but the sending-off has changed the game."
Colchester: Davison, Halford, Baldwin, Brown, Barker, Duguid, Jackson, Izzet (Jones 76), McLeod (Watson 68), Iwelumo (Guy 87), Cureton.
Subs Not Used: Gerken, White.
Sent Off: Barker (78).
Booked: Barker, McLeod.
Goals: Halford 68, Baldwin 74, Cureton 85.
Southend: Flahavan, Francis, Sodje, Prior, Hammell, Campbell-Ryce, Maher, McCormack (Riera 80), Gower, Eastwood (Hooper 88), Harrold (Bradbury 62).
Subs Not Used: Cole, Clarke.
Sent Off: Maher (51), Gower (56).
Booked: McCormack, Gower.
Att: 5,954.
Ref: S Bennett (Kent).