Four goals in a sorry 24 minute spell in the second-half left the Silkmen shell shocked. They had enjoyed the better of the opening exchanges but yet again this season failed to take advantage.
Early in the second minute Allan Russell glanced wide from six yards, then in the eighth minute he scuffed a low drive across the face of goal. Set up by Paul Harsley in the 21st minute, he then hoofed a 15-yard volley over the bar.
But their best chance fell to centre back Tony Barras, whose close-range header was only denied by a finger-tip save from Mark Tyler.
Peterborough nearly scored moments before the break when David Farrell blazed over the bar from the edge of the box.
The floodgates opened after the break when 19-year-old Danny Crow waltzed through the centre of the defence before rifling a low drive past Alan Fettis. The veteran keeper was then at fault in the 67th minute when he allowed a snap shot from Farrell to slip through his fingers.
Three minutes later, Adam Newton crossed to the far post for Lee Thorpe to head back across goal for Farrell to bag his second from close range.
Worse was to follow for Macclesfield as they allowed Thorpe the freedom of Cheshire to pick out sub Calum Willock, who brushed the ball in from close range.
Peterborough might have added another deep in injury time but James Quinn saw a 15-yard shot ricochet wide off the keeper's legs.