By the time Kevin Maher was sent off for two yellow cards midway through the second half the Daggers had already struck three times, two of them from corners, and despite Tom Craddock's second of the match setting up a nail-biting finale they held on to secure a much-needed in.
The home side, without a win in three games, took the lead on 36 minutes when Sam Williams headed in Matt Saunders' corner. But Oxford striker James Constable was kicking himself that he didn't put away one of two good chances when through on goal before the match exploded into life with four goals in 11 minutes early in the second half.
First Luke Howell followed up Gayle's shot to put Dagenham two up and then Tom Craddock pulled one back with a superb hooked volley from Sean Rigg's cross.
But the Daggers punished Oxford from a corner again as Luke Wilkinson powered home a free header. It was then Oxford's turn to score through Craddock's second after a poor back-pass to give the U's hope.
But despite late pressure they couldn't break through again, with Dagenham keeper Chris Lewington saving brilliantly from Adam Chapman in the final minute.