George Williams scored in the 89th minute to secure a vital 1-0 win for Barnsley against 10-man Peterborough in their pursuit of a Sky Bet League One play-off spot.
Chris Forrester had controversially seen red for Peterborough two minutes before half-time, receiving two yellows within 20 seconds of each other after a face-to-face confrontation with Conor Hourihane.
The win puts Barnsley level on points with play-off rivals Gillingham, who drew 1-1 at Rochdale, but Barnsley had to play a patient game after seeing Posh goalkeeper Ben Alnwick deny them a number of times.
The home side thought they had gone ahead shortly after Forrester's sending-off when Josh Brownhill cut in from the left and fired the ball towards goal, only to see Alnwick deny him.
The resulting corner was just as dangerous, Roberts nodding the ball into the same corner, only to be denied again.
Just when the game looked destined for a draw, Williams made the Barnsley pressure pay, nodding in from Adam Hammill's cross with just minutes remaining.