Southend ended Oxford's three-game winning streak with a 2-0 win - a repeat of their scoreline at Cheltenham in their last match on December 14.
Two first-half goals did the trick, though the second one looked a fluke.
Barry Corr fired them into the lead on 18 minutes with a low shot through a sea of legs after Blair Sturrock saw his shot blocked following a corner.
Right-back Sean Clohessy doubled the Blues' lead when his cross from near the touchline 35 yards out drifted over Oxford keeper Ryan Clarke and went in off a post.
And his reaction indicated he hadn't meant it as a shot.
Oxford seldom got their game going, though James Constable planted a header wide from Ben Purkiss's cross in the first half, and Steve Maclean was unlucky with a far-post header that came back off the woodwork.
Southend controlled the midfield, however, and in the second half, as Oxford pressed forward, they had further chances on the break, with Clarke saving from Sturrock and Corr.
The busy Sturrock also went close when he lobbed goalkeeper Clarke in the dying seconds.
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