The 29-year-old's tap-in from Lee Frecklington's cross saw the visitors walk away with all three points in the South Yorkshire derby at Hillsborough.
Michael Turner thought he had brought the hosts level before half-time but was adjudged to be offside.
Goalkeeper Lee Camp pulled off a number of saves as the Millers held on.
After a poor first-half display, the home side bombarded Rotherham's goal for the second 45 but Camp was equal to the task.
The 31-year-old shot stopper denied Gary Hooper and Lucas Joao before stopping Ross Wallace's stinging free-kick with his feet.
As the Owls continued to search for a much-needed equaliser, following Cardiff's victory in the early kick-off, Wallace was unlucky to see his thumping strike cannon off the woodwork.
Sheffield Wednesday remain in the play-off places, level on points with Bluebirds, and just a point ahead of Birmingham and Ipswich - who both have a game in hand.
Meanwhile, a win for ex Sheffield United manager Neil Warnock with his new club saw Rotherham register their first consecutive victories since December but they remain three points adrift of safety.
Sheffield Wednesday boss Carlos Carvalhal: "It was frustrating we didn't score of course. We expected to win the game, we prepared for the game to win and it's a game that was a little strange for us.
"For the goal we had ruled out in the first half, to me it is not offside. There was one defender in line with him (Michael Turner) and that is why the referee gave it as a goal and the assistants didn't give offside at first.
"But I don't want to talk too much about referees. I love football and I just want to talk about football."
Rotherham manager Neil Warnock: "You don't overcome your rivals every week, so it is special, because they aren't a bad side. That makes it better for me.
"I thought we got it spot on tactically today, too. Other than the one they hit the bar with, I can't remember anything too clear-cut for Camp to deal with.
"I thought we restricted their play and it will probably be their most difficult game for the rest of the season.
Matt Derbyshire's first-half goal was enough to help relegation-threatened Rotherham earn a victory against play-off hopefuls Sheffield Wednesday.