The visitors dominated the first half of Saturday's League Two clash at Roots Hall and it was only some good saves from on-loan West Brom goalkeeper Luke Daniels that kept the scores level as he denied Peter Leven three times and Andy Whing once.
The Shrimpers took the lead against the run of play in the first minute of stoppage time when Ryan Hall whipped in a free kick from the left and Mark Phillips headed home from close range at the back post.
Michael Timlin blew a good chance to double Southend's lead and Oxford rubbed salt in the wound by equalising in the 62nd minute.
Leven's diagonal cross from the left picked out Damian Batt at the back post and he headed back across the goal into the left-hand side of the goal.
Parity lasted just five minutes though before Hall restored Southend's lead with a superb arcing 25-yard shot that went in the top left-hand side of the goal following Timlin's pass.
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