James Constable scored twice to help Oxford to an impressive victory at play-off hopefuls Exeter.
Jamie Cureton had hit the bar for the hosts before Constable lashed home the opener from Tom Craddock's lobbed pass.
Constable latched on to a poor defensive header from Pat Baldwin for his second before Peter Leven made the points safe with a low shot.
The Grecians pulled one back when Cureton converted a penalty after Damian Batt had handled.
Oxford handed a debut to former Oldham forward Josh Parker, who joined on non-contract terms last week.
VIEW FROM THE DRESSING ROOM
Exeter boss Paul Tisdale told BBC Radio Devon:
"It's my job to try to alter this trend we have of results at home. There weren't many positives, but our first 20 minutes was the best we've had at home all season. We were the side most likely to score.
"But we've failed too many times in our home games. There's something I need to do about it. It's a bit of a Rubik's Cube at the moment, but we'll sort it out.
"I don't think for the last month we've been able to get on a grass pitch and do our training. We've been indoors, up the forest and the heath, and it doesn't look like that's going to change so we just have to do what we can do on Saturday to reverse this trend."