Oxford cruised past nine-man Burton to keep up their hopes of making a late play-off push.
Steve MacLean put the hosts in front when his shot deflected past Brewers keeper Adam Legzdins.
Darren Moore saw red for bringing down James Constable in the area and from the resulting penalty Tom Craddock slotted home.
Tom Parks was given his marching orders for a second bookable offence before MacLean lashed in a late third.
Burton Albion manager Paul Peschisolido told BBC Radio Derby:
"I don't like harping on about bad luck. We have to keep going and trying to make our own luck.
"And, if we keep doing that right, eventually things will change.
"I want to see the strong lads stand up and be counted and say 'Yes, we have injuries and suspension but pick me and I'll be the man to make sure things are rectified'."