George Boyd's superb strike earned Peterborough victory over his former club as Nottingham Forest failed to score for a sixth consecutive match.
Boyd curled in the winner from 18 yards to secure back-to-back wins for Posh for just the second time this season.
Emile Sinclair and Paul Taylor both nearly added to the lead.
But the hosts wasted several chances to equalise, Marcus Tudgay having a header cleared off the line and Lewis McGugan twice going close.
Forest once again created plenty of opportunities without taking any.
Despite manager Steve Cotterill insisting their luck will turn, they remain in the Championship relegation zone after a fifth defeat in six matches.
Their cause was not helped by an early injury to Paul Anderson, although his replacement, Garath McCleary, nearly put the hosts ahead with a 20-yard effort that produced a decent save from Joe Lewis.
But the visitors began to get on top and Taylor worked Lee Camp with a shot from outside the area before ex-Forest loanee Boyd fired in the only goal of the game.
Sinclair then went close and Taylor forced Camp in to action save with a shot from the edge of box.
Taylor worked Camp again at the start of the second half before Forest almost equalised when Tom Kennedy hacked a Tudgay header away to safety.
The hosts responded and McGugan shot over before squandering a glorious chance, lifting the ball over the bar after being put through by Dexter Blackstock.
Taylor and Tommy Lowe had opportunities to double Peterborough's lead but both missed the target, while Forest's best late effort saw McCleary power a close-range header straight at Lewis after good work by substitute Andy Reid.
Nottingham Forest manager Steve Cotterill:
"We didn't deserve to get beat but it's pretty obvious that we are struggling to put the ball in the net.
"We put enough balls in their box to have got something from it and we've got to stick our necks on the line to make sure that we do.
"We need one to drop for us but it's important that we stay strong and come through it. We will keep doing what we can to change things and hope that we get people fit as soon as possible."
Peterborough manager Darren Ferguson: "Boydy is capable of that but for one reason or another Forest didn't see that when he was here on loan.
"We know the ability he has got and it was a superb effort. I'm just disappointed we didn't add to it and win the game more comfortably.
"We had injury problems today - I nearly had a chance of playing myself - but the lads who came in did really well and took their opportunities.
"It's a win that will give the players a lot of belief. I thought we were comfortable and were a real threat on the counter-attack throughout the game."