Alfie Potter pounced shortly before the break to hand Oxford a deserved 1-0 victory at Dagenham.
Dagenham's run of miserable form continues, with the club still needing points to make sure of their League Two status, while the visitors secured a welcome first win in six games.
Oxford went in front five minutes before the break in what was an entertaining first half.
Deane Smalley whipped in a cross for Potter, who swivelled neatly before smashing home to register his 10th goal of the season.
The Daggers had earlier seen Luke Wilkinson drive over the crossbar from 30 yards, while the U's replied with Andy Whing planting a downward header inches wide.
Daggers' Jake Reed found himself clear of the Oxford backline only to drive a low shot past the far post from an acute angle.
After the restart, Dagenham sub Mo Shariff found space but his shot was deflected just wide.
Oxford hit back and sub Sean Rigg almost had an immediate impact when he missed from close range after latching on to Potter's driven cross into the box.
Shariff then missed a great late chance to level it up for the hosts, who remain 17th in the table.