The 34 year-old, son of Manchester United's Sir Alex Ferguson, left coach Tommy Taylor in charge and despite a bright start Posh defensive problems were shown-up as Stockport finally found some form on the road and took command with first half goals from Anthony Elding and Michael Rose before substitute Adam Griffin wrapped up victory with a third at the end.
Long serving Posh goalkeeper Mark Tyler, who signed a new three year contract immediately before the game, was soon in action, getting down well to stop Adam Proudlock's 12 yard drive after barely two minutes. Posh then had a let off when Anthony Pilkington rattled a post with a fierce rising drive before Tyler flung himself to stop an Elding effort.
Stockport broke the deadlock on 20 minutes, an unmarked Elding, snapped-up from cash strapped Boston for £55,000 earlier in the month, netting with a far post header following a towering corner by Stephen Gleeson.
Stand-in County goalkeeper Wayne Hennessey , who used his body to block an early blast from Micah Hyde, prevented a home equaliser when dropping on Aaron McLean's shot on the turn just before Stockport doubled their advantage with a spectacular 25 yard free kick by Michael Rose.
Posh seemed harshly penalised by referee Jamail Singh, but Rose stepped forward and sent a right footed free kick soaring out of Tyler's reach and into the top left hand corner of the net.
Things did not improve for Posh after the break and County could well have added to their advantage when defender Jason Taylor hit the woodwork and Tyler did well to deny Pilkington before he was substituted late on.
Stockport's third successive league victory was assured in the 90th minute with Griffin finding the far corner of the net with crisp drive that flashed out of Tyler's reach.