First half goals from Simeon Akinola and Timothee Dieng consign U's to defeat in the Essex Derby.
The U's lined up at Roots Hall with Steve Ball opting for three changes to his team on Boxing Day.
Junior Tchamadeu, Cohen Bramall and Callum Harriott were out of the starting eleven, with Omar Sowunmi, Ryan Clampin and Kwame Poku coming into the line up.
It was a quiet and understated start to what would normally be a lively and loud affair. Southend looked to get forward, with the U's happy to let them have the ball in the opening minutes.
But the U's were made to pay early on, after giving away a cheap free kick on the edge of the area. The ball was lofted in, with the unmarked Simeon Akinola heading past Gerken who could do nothing about it.
The Shrimpers extended their advantage ten minutes later, with Timthee Dieng finding the net this time. Kyle Taylor ran through the centre of the U's midfield, sliding the ball through to Dieng who tucked the ball into the far corner of the net, beyond Dean Gerken.
Jevani Brown went closest yet for the U's to reducing the defecit with just under half an hour played. He controlled a cross from Kwame Poku well and turned to shoot, but couldn't quite find the target.
The U's went even closer just before the break when Kwame Poku rattled the woodwork. He cut in from the right wing after riding a challenge from Demetriou and struck the ball well, beating Oxley but not the far post before the home side were able to clear.
But Steve Ball's side were unable to get a goal back before half time, and headed to the dressing room two goals down.
The U's had a good chance to pull one back five minutes into the second half with Courtney Senior, but he was unable to control the ball at the far post before he was tackled.
Ball and Mullins opted for changes to try and bring their side back into the game with half an hour of play to go with Lapslie and Gambin brought on in place of Poku and Stevenson.
The U's were seeing more of the ball in the second half, and in more dangerous positions than they had before, but still seemed to lack a punch that would break through the home defence.
A final further change was made, in the shape of Josh Bohui coming on for Michael Folivi for the final ten minutes, but the third sub was unable to make a real difference at Roots Hall.
The full time whislte blew with Southend United taking all three points.
Southend United starting XI: Oxley, Bwomono, Hobson, Dieng, Akinola (Acquah 73'), Egbri, Nathaniel-George (Howard 88'), Demetriou, Taylor (Halford 80'), Hart, White.
Unused subs: Seaden, Phillips, Sterling, Walsh.
Colchester United starting XI: Gerken, Smith, Sowunmi, Senior, Brown, Chilvers, Eastman, Clampin, Poku (Gambin 60'), Stevenson (Lapslie (64'), Folivi (Bohui 79').
Unused subs: George, Welch-Hayes, Tovide, Sayer.