Nottingham Forest remain in the bottom three after their sixth game without a goal gave Peterborough all three points.
Forest started well and had chances to take an early lead, but when a goal for Peterborough put them in front Forest lost their way and finished the half the weaker side.
Forest impressed at the start of the second half, creating some good football and after a quiet period a late flurry gave the fans brief hope of an equaliser but it wasn't to be.
There was just one change to the starting line-up with Joel Lynch injured and, with Brendan Moloney also unavailable, Guy Moussi took his place in defence.
And Forest's worries increased when Paul Anderson, who had apparently tweeked a hamstring in the warm-up, had to be substituted just five minutes into the game, being replaced by Garath McCleary.
Chris Gunter created a chance for Forest with a blistering run down the right to get on the end of a long cross from Jonathan Greenings. He squared the ball into the penalty area but it was just too high for Marcus Tudgay.
But Forest kept possession and Lewis McGugan was able to skip past a defender and shoot from 20 yards, forcing Joe Lewis to parry the ball away.
As Forest kept up the pressure, McCleary also came close with a powerful long-range shot and Lewis had to dive to his left to attempt the save, but the ball was deflected out for a corner.
But it was Peterborough who took the lead, 20 minutes into the game, with their second shot of the half when Craig Alcock got away down right and pulled the ball back for George Boyd, who was given too much time and space to chip the ball into the top corner from the edge of the box.
Peterborough looked the better team after the goal, before Forest began to get back into it and McCleary came close when he got his head on the end of a corner and his effort was only just wide.
And McCleary continued to impress with a great run down the right, beating several players but the final ball let him down as it landed on top of the net when he could have put it at the feet of Dexter Blackstock.
Peterborough threatened again seven minutes before the break when Paul Taylor found himself enough space to get a shot in and Lee Camp did well to parry the ball away.
And Forest got themselves in trouble again at the start of stoppage time when Emile Sinclair got away, forcing Camp to come right out of his goal to make the save, parrying the ball away as Sinclair tried to get round him.
Radi Majewski was replaced by Andy Reid for the start of the second half.
Forest looked far more positive as the half got under way, pushing forward from the outset and going in strongly for the ball in midfield.
Good work by Jonathan Greening won Forest a corner and from Reid's ball in Tudgay's header was cleared off the line by Ryan Bennett.
McGugan missed Forest's best chance of the game when he got on the through ball from McCleary and ran clear only to chip over the crossbar with a half volley.
Forest continued to threaten, pushing forward again and again, with Reid impressing since coming on and giving the away side problems.
Matt Derbyshire became Forest's final substitute, replacing Tudgay up front in the 69th minute.
Peterborough missed the chance to finish the game off when Daniel Kearns was allowed to get forward, sending the ball through to Taylor but his effort from the edge of the penalty area was off target.
And Camp had to made a good save, beating the ball away for a corner to prevent Tommy Rowe from finding the garget.
Forest had the chance of a late equaliser when Reid crossed from the left to the back post Reid cross from left to back post where Blackstock sent the ball back across to the near post for McCleary whose effort went straight into chest of Lewis from 2 yards out.
And in the 90th minute, from Reid's corner, Derbyshire's header scraped the crossbar and landed on top of the net.
And late in stoppage time Reid again crossed from the left and in a crowded box Blackstock headed back across goal and was cleared as far as McGugan who missed his volley.
Nottingham Forest: Camp, Chambers(C), Moussi, Gunter, Cunningham, Greening, Majewski(Reid 45minHT), Anderson(McCleary 6min), McGugan, Tudgay(Derbyshire 69min), Blackstock
Subs not used: Smith, Findley
Bookings: McGugan 34min
Peterborough United: Lewis, Bennett, Zakuani, Wootton, Boyd(C), Sinclair(Tomlin 72min), Rowe, Kearns(Newell 90min), Taylor, Alcock, Kennedy
Subs not used: Jones, Thompson, Jones, Lawler
Bookings: Sinclair 63min
Scorer: Boyd 20min
Referee: O Langford
Attendance: 24,376 Away attn: 2,655