A Marc Richards brace helped Chesterfield to a first win in four games as three goals in eight minutes saw off Northampton.
Jay O'Shea celebrated his permanent deal by finishing from 10 yards after combining with Danny Whitaker.
A Clarke Carlisle error allowed Richards to fire low into the net, before Tendayi Darikwa released the striker to slot past Lee Nicholls.
Northampton came close to a consolation when Chris Hackett hit the crossbar.
VIEW FROM THE DRESSING ROOM
Chesterfield manager Paul Cook told BBC Radio Sheffield:
"We are delighted - it felt like two games we lost in a quick couple of days to Accrington and Wycombe.
"We're a club that expect to win football games and we've worked hard all week.
"The lads were a credit today, we had loads of good players, loads of good performances and it was a very good win against a very good side.
"We looked really good on the break and counter-attacking."
Northampton Town manager Aidy Boothroyd told BBC Radio Northampton:
"It's a missed opportunity. When you go on a little run, you build a reputation.
"The team that you play against up their game because they're frightened of you.
"I'm thoroughly disappointed because we never started for 30 minutes. It was unacceptable. We were mentally lazy - they were up for it and we were complacent.
"We got a hiding, we have to take it but we're better than that."