Dave Kitson's penalty earned Reading a third win in four matches as they worked hard to outdo a battling Rotherham side at the Madejski Stadium.
He rammed home his spot kick on the stroke of half time after Chris Swailes had fouled Nicky Forster. His single strike proved to be enough to clinch all three points in a game of few chances.
The Royals made a poor start to the game, barely creating anything in the opening 30 minutes as the visitors sat back and looked to counter attack through pacy forwards Barker and Mullin.
The tactic worked for long periods and in the early stages it was Ronnie Moore's side who carried the greater threat.
Chris Sedgwick skied a shot when Adrian Williams' poor clearance from a Richard Barker cross fell invitingly for the Rotherham midfielder.
And Scott Minto saw a stinging free-kick parried by Reading keeper Marcus Hahnemann, who reacted well to bravely dive at the feet of Richard Barker on the follow up.
Yet it was Reading who thought they had made a breakthrough on 20 minutes when James Harper's swinging free-kick was turned home by Kitson only for an offside flag to deny the striker his second goal of the season.
Kitson did not have to wait too long to register that particular statistic, as he gratefully accepted the chance to break the deadlock from the penalty spot a minute before the break after a fierce argument with Nicky Forster.
Forster had looked poised to shoot when Rotherham's skipper Chris Swailes took his standing leg away. Referee Lee Probert, widely booed by the home crowd for a string of poor decisions, pointed to the spot and then booked Shaun Barker for protesting a little too much.
Kitson blasted the ball low and centrally to put Reading in front.
The home side might have double their lead when Steven Sidwell saw a searching long-range drive plucked out of the air by Rotherham keeper Mike Pollitt in a largely quiet second half.
And the alert keeper rescued Rotherham again when an offside flag surprisingly did not come to their aid midway through the second half, the keeper diving at Forster's feet after a clever flick from Kitson had sent him clear.
But the lively Paul Shaw, despite slipping back into midfield to accommodate the arrival of striker Michael Proctor from the substitute's bench, should have restored parity for the Millers when he found space in the area but blazed wide from an increasingly tight angle.
Ronnie Moore's side pushed for an equaliser late on, with the skilful Proctor showing some good chances. But despite looking set to throw the game away, the Royals secured the three points and third place in the league.