Posh, already guaranteed a top-six spot prior to kick-off, fell behind after just 14 seconds at Spotland when Joe Lewis collected a Gabriel Zakuani backpass and miscued his clearance straight to Jean-Louis Akpa Akpro, who steadied himself before side-footing into the top corner of the net.
"Their opening goal was embarrassing," said Ferguson, whose side drew 2-2. "It was a very unprofessional start from us and they made us pay.
"That took us a good half-hour to recover from. We got a little bit of control over the game with the goals either side of half-time but to lose a goal as easily as we did, I'm not sure what was going on there.
"I want to go into the play-offs able to play three or four formations and we need a point to secure fourth place and that would give us a night game at London Road.
"But we'll have to play better than we have been doing. We've missed out on automatic promotion and have had to deal with that disappointment but we're not winning games and we want to be going into the play-offs winning games."
Source: PA
Source: PA