Two goals from Wayne Purser and another from Richard Logan condemned Chesterfield, who also had substitute Caleb Folan sent off for an off-the-ball incident with Mark Arber, to defeat.
Gareth Davies did pull a goal back for the home side but any chance of a recovery vanished when Purser scored his second in the 62nd minute.
Peterborough went into the game with the worst away record in the division and they looked set for another fruitless afternoon as Chesterfield pushed them back.
But the visitors struck in the 12th minute with their first attack when Purser got behind the defence from the right and pulled the ball back for Logan to drive the ball into the top left-hand corner from six yards.
Purser doubled Peterborough's lead two minutes later when Chesterfield failed to clear a free-kick in from the right and the striker knocked the ball over the line with the home players appealing for offside.
Substitute Davies pulled a goal back in the 23rd minute when Mark Tyler made a good save from an Aaron Downes' header, but the ball was squeezed in by the midfielder from a tight angle.
Ian Evatt was close to an equaliser when his 40th minute header was held on the line by Tyler, but Chesterfield hardly troubled Peterborough after the break.
Purser turned substitute Steve Blatherwick on the edge of the area and finished clinically from 12 yards to restore his team's two-goal cushion and, two minutes later, Folan was red-carded.
Referee Tony Bates consulted with a linesman after the striker clashed with Arber and then sent Folan off despite protests from his team-mates.
Any chance of a late recovery was snuffed out when Tyler made an excellent block from Mark Allott in the 82nd minute but after that it was easy for Peterborough as Chesterfield slumped to another home defeat.