It took the Millers only four minutes to go ahead, Daniel Nardiello converting a penalty after he was pushed by Brewers defender Zander Diamond.
Seven minutes later it got even better - Kari Arnason's long throw caused panic in the Burton defence and, when Ben Pringle's shot looped up off a defender, Kayode Odejayi was left with a simple headed finish.
A great block by Michael O'Connor denied Albion's Billy Kee but after 29 minutes Odejayi should have had a second when he nodded Nardiello's cross over the bar.
Things got worse for Albion shortly before the hour when Robbie Weir was sent off for collecting his second yellow card in as many minutes for fouls on Ben Pringle and David Noble.
Rotherham made it three after 74 minutes when Pringle's cross took a wicked deflection off Anthony O'Connor to find the back of the net.
As the hosts threatened to run riot, Burton goalkeeper Ross Atkins denied Nardiello with a great save and followed it with an even better one from substitute Alex Revell.