Rotherham United's relegation woes worsened and Barnsley's play-off hopes were lifted as the visitors won the South Yorkshire Championship derby at New York Stadium.
The Millers' performance in a hard-fought clash was nothing like their August capitulation at Oakwell when they lost 4-0.
But a 69th-minute goal from Adam Armstrong earned the visitors South Yorkshire bragging rights, leaving the home side 11 points adrift of safety.
Rotherham had their full share of chances but Paul Heckingbottom's side enjoyed more control after the break and move within a point of the play-offs.
Armstrong took advantage of Ryan Kent's sublime, defence-splitting pass to steer the ball beyond home goalkeeper Richard O'Donnell to send the away following into raptures.
Both sides had opportunites to score in a fairly even first half.
Jon Taylor wasted an inviting seventh-minute opportunity for Rotherham when he failed to get his shot away after being played in by Danny Ward and Joe Mattock struck the post from distance nine minutes before the break.
Millers old boy Aidy White shot across goals and wide for the visitors after 20 minutes and on the half-hour mark Armstrong grazed the bar when he got in behind substitute centre-half and tried his luck from just outside the penalty area.
Armstrong struck the decisive blow after Ward had tested Reds keeper Adam Davies with a deft chip and Davies had been equal to Jerry Yates' free header.
Millers midfielder Tom Adeyemi has been ill during the week and had to settle for a place on the bench as the home side went 4-4-2 and played Ward and Yates up front.
Barnsley handed a debut to midfield loan signing Matty James, but fellow midfielder Alex Mowatt's move from Leeds United went through too late for him to be considered.
There wasn't a great deal in it, but Barnsley march on after the departure of key man Conor Hourihane to Aston Villa while the gap between Rotherham and survival grows.
Rotherham United (4-4-2): O'Donnell; Fisher (Allan 77), Wood, Belaid (Kelly 26), Mattock; Forde (Bray 86), Smallwood, Vaulks, Taylor; Ward, Yates. Subs not used: Bilboe, Blackstock, Adeyemi, Warren.
Barnsley(4-4-2): Davies, Jones, Roberts, MacDonald, White (Evans 60); Watkins, Scowen, James, Kent (Hammill 86); Armstrong (Williams 81), Bradshaw. Subs not used: Townsend, Moncur, Jackson, Payne.
Goals: Armstrong 69 (Barnsley).
Referee: Keith Stroud (Hampshire).
Attendance: 11,050 (2,601).