Opportunistic Ricky Holmes and Simon Ferry strikes either side of the break helped seal Portsmouth's first away win of the season at Burton.
Holmes latched onto a Jordan Pickford save from a Patrick Agyemang header to put the visitors ahead.
Ferry then pounced on another Pickford save to stab in from close-range.
Pompey defender Yassin Moutaouakil was red carded late on for a kick on Jimmy Phillips before Zander Diamond netted a consolation goal for Albion.
VIEW FROM THE CHANGING ROOM
Burton manager Gary Rowett told BBC Radio Derby:
"We've not done enough to win the game I believe.
"At home we've just not quite played with anywhere near the intensity and brightness that we did last season.
"We knew that would be difficult to replicate and we've been better away from home certainly so far but at home we've just not created enough chances I don't think.
We've not worked hard enough to create the chances. We're not getting the rub of the green at the minute. You can certainly argue with that about the second goal. I just cannot understand for the life of me but that was a foul."
Portsmouth manager Guy Whittingham speaking to BBC Radio Solent:
"It's very pleasing because we've done a lot of hard work during the week, you know when we have leads, how to protect them and I think we did that very well today.
"It's probably the game, out of all the games we've played so far, we've probably created the least amount of chances for us, but that's the balance we're looking for; where you create chances, you score goals and you also have to make sure that you're hard to beat."
(On missing out on a clean sheet) "Again, we've conceded with 10 men. Who knows if we'd have seen it out with 11 but we'd like to have thought so."
(On Yassin Moutaouakil's red card ) "You know in football if you're a footballer you can't kick out at people no matter how much you're wound up or you think you've had injustice, you can't do that, so the referee was left with no choice."