Darren Ferguson's men suffered a sixth defeat of the campaign following a 2-1 home defeat to Scunthorpe United.Peterborough United suffered a 2-1 defeat to another side struggling near the foot of the Sky Bet League One campaign following a disappointing display at London Road.
On 14 minutes, the visitors opened the scoring as Luke WILLIAMS was able to burst into the box, ride a poor challenge from Jack Baldwin and slice an effort past Alnwick and into the back of the net.
The lively Nathaniel Mendez-Laing saw a deflected shot pushed around the post by Slocombe after cutting inside from the left as Posh tried to get back on track.
A header from Newell was plucked out of the air by Slocombe after a good knock back across goal from Jon Taylor on 24 minutes.
Posh were forced into a change on 40 minutes as Conor Washington replaced the injured Jack Baldwin.
Taylor headed wide after a Mendez-Laing shot had been deflected into his path.
Madden was denied by the legs of Alnwick before Lyle Taylor smacked the bar from close-range after a strike from McSheffery was parried by the Posh goalkeeper.
Osbourne was next to be denied by Alnwick, his long-range strike parried by the Posh keeper. At the other end, Taylor was superbly denied by the Iron keeper after a good burst into midfield by Newell before Mendez-Laing's low centre eluded everyone.
On 57 minutes, Posh levelled the scores as a poor clearance from Slocombe was cushioned into the path of WASHINGTON by Bostwick and the substitute coolly converted past the keeper.
However, Posh only held the lead for five minutes as an effort from OSBOURNE deflected into the back of the net past a flat-footed Alnwick via the boot of Santos.
Final Score: Posh 1-2 Scunthorpe United
Posh: Alnwick, Smith, Newell, Burgess, Baldwin (sub Washington 40min), Bostwick, Santos, McCann (sub Anderson 58min), Taylor, Mendez-Laing, James (sub McEvoy 75min). Unused subs: Henry, Oztumer, Zakuani, Ferdinand.
Scunthorpe: Slocombe, Madden, Bishop, Williams (sub McAllister 86min), Taylor (sub Kee 71min), O'Neill, Boyce, McSheffrey, Williams, Llera, Osbourne. Unused subs: Weaver, Myrie-Williams, Hawkridge, Adelakun, Wootton.
Attendance: 6,275 (486 Scunthorpe fans)