Cobblers boss Jimmy Floyd Hasselbaink felt his side paid the price for not taking their early chances in the Easter Monday game at Peterborough.
“The result is very disappointing but I thought we played really well,” he said.
“We looked bright, we were sharp and we created chances. Peterborough scored in our best spell and that is the killer for us. Both goals came from long balls and if you defend like that you are going to minimise your chances.
“We don’t kill teams off and that’s why we are where we are.
“It’s very tough at the moment and we aren’t doing the simple things right.
“I felt Ash Taylor was unlucky with the red card, Leon Barnett was next to him and we are going to challenge that decision.
“Today is another tough one to take but I will fight to the bitter end, I’m not the type of person to give up.
“It is going to be difficult but we need to believe. Nobody is going to help us, we’ve got to stop feeling sorry for ourselves and I believe we can do it.”