Second-half goals from George Donnelly and Bobby Grant helped Rochdale beat Oxford to move into the play-offs.
The U's came close to breaking the deadlock early on, with Tom Craddock having a close-range header cleared off the line by Rhys Bennett.
They were made to pay when sub Donnelly rose highest to meet Grant's left-wing cross to put Dale ahead.
And Donnelly returned the favour when his driven cross was tapped home by Grant to seal the victory.
VIEW FROM THE DRESSING ROOM
Rochdale manager John Coleman told BBC Radio Manchester:
"The lads were under no illusions what was demanded of them and I think they delivered.
"We were a little bit edgy in the first half but we came through it.
"Give Oxford their due, they took the game to us, but we stuck to our guns and we just about shaded it in the end.
"Anyone who knows me knows I don't really like making subs. Sometimes they work, sometimes they don't, and tonight it worked for us."
Oxford United manager Chris Wilder told BBC Radio Oxford:
"No disrespect to the opposition but I think we played like the home side tonight.
"I'm struggling to find a way to explain how we have not won this game by two or three.
"We dominated the second half and chased the game and got done twice. We were the architects of our own down fall.
"The performance was pretty good and I think if we would have shown more quality from our front four then we would have gone home comfortable winners tonight.
"It is frustrating and we have to show the consistency in results and be better in the final third."