Jamie Cureton hit a superb hat-trick in a Colchester victory which deepens Southend's relegation worries.
It took only 38 seconds for Cureton to open his account when he volleyed a crisp, right-footed shot into the bottom corner from 18 yards.
Then on 63 minutes, Cureton notched his second when he drilled a fierce 25-yard effort into the top right corner.
The striker sealed a fine display 12 minutes from time when he clipped in his third from inside the box.
Southend boss Steve Tilson:
"We'll always keep believing we can avoid relegation. The players are deflated but there are five games to go.
"Their first goal knocked the stuffing out of us. You prepare all week and then within a minute you go behind to a dreadful goal.
"There's not a lot between the top and the bottom. That first goal cost us."
Colchester boss Geraint Williams on hatrick hero Jamie Cureton:
"He showed he's a natural goalscorer with the early chance. He works the lines and darts in.
"He's not the biggest so there's no point him standing up to people - and if we can find him he'll usually score.
"The strikers are getting all the plaudits, and rightly so, but the defence has also been excellent."
Southend: Flahavan, Hunt, Sodje, Clarke, Hammell (Harrold 77), Gower, McCormack, Maher, Foran (Campbell-Ryce 46), Eastwood, Bradbury.
Subs Not Used: Collis, Barrett, Francis.
Booked: Maher, Harrold.
Colchester: Gerken, Duguid, Baldwin, Brown, Barker, Garcia (White 88), Watson, Izzet, Jackson, Cureton (Ephraim 83), Iwelumo (Guy 72).
Subs Not Used: Davison, Elokobi.
Goals: Cureton 1, 63, 79.
Att: 10,552
Ref: K Friend (Leicestershire).