Barnsley's play-off hopes appear in tatters after they followed up their 6-1 drubbing at Grimsby with a dismal home defeat against struggling Peterborough.
The one dimensional Tykes have now just won once in their last 13 games and look in free fall down the table, putting manager Gudjon Thordarson under increasing pressure.
Barnsley had three strikers on show, with on loan Daniel Nardiello by far the livelier of the trio, but they received little service from a home midfield lacking in confidence.
Barnsley did start brightly enough and perhaps should have lead inside the opening 15 minutes.
Kevin Betsy sent a close range header thudding against the bar on four minutes before sending an even better headed opportunity soaring over the top.
Nardiello did have the ball in the Peterborough net but the flag was already up for off side.
Peterborough showed little in attack during the first half, although central defender Mark Arber squandered a great chance two minutes before the break when his weak shot was easily saved by Marlon Beresford.
The only goal arrived just 30 seconds after the break when a number of errors in the Barnsley defence saw Peterborough break forward and striker Calum Willock saw his miss timed volley squeeze in at the far post.
Barnsley looked drained after that and visiting striker Clive Platt almost added to their woes with a header that was cleared off the line.
Barnsley almost grabbed a last minute equaliser when Betsy dug out a deep cross which Nardiello failed to convert when well placed at the far post.