Northampton manager Aidy Boothroyd accused his team of believing their own hype after they were beaten 3-0 by Chesterfield.
The game was decided in the space of eight minutes when midfielder Jay O'Shea opened the scoring before Marc Richards bagged two goals to give the Spireites their first win of 2013.
Boothroyd admitted: "When you go on a little run and people start to talk about you, you have an opportunity to build a reputation and that reputation can sometimes be better than you actually are.
"I am thoroughly disappointed because we never played for 30 minutes and you can't do that against teams that are up for it. You have to give credit to the opposition but we were complacent and thought we were better than we were for 30 minutes.
"We got a good hiding and when you get a good hiding, you have to take it. We have to make sure we learn lessons from this. We've still got a lot of work to do and that first 30 minutes was unacceptable in so many ways."
Spireites boss Paul Cook praised his side's all-round performance.
"We worked hard all week on how we could affect the game in terms of moving the ball and passing and I thought the lads were a credit. There were lots o good performances and it was a very good win against a very good side.
"We had numerous chances and looked really good on the counter attack and got forward quickly. We want to play a passing game and press the ball and we did all the things we wanted to do.
"We must be strong without the ball and without possession because we do have players who can play with a little bit of flair and we did that.
"We've had a lot of chances in the last two games so to score three goals and get a clean sheet is pleasing."