A deeply disappointed Keith Curle accused his players of allowing Scunthorpe 'to do what they wanted' during Saturday's torrid 3-0 defeat to the Iron.
The Cobblers were slack to get going at Glanford Park and paid the price when Lee Novak scored twice in the first 14 minutes, both times capitalising on soft defending.
Kevin van Veen's fine strike made it 3-0 by half-time and the visitors' disastrous day was complete when Vadaine Oliver saw red in the second-half.
"Disappointed doesn't cover it - it's worse than that and a lot worse than that," said Curle.
"I've got to say how I see it and we had a 20-minute spell where their attackers were better than our defenders and all game I don't think our attackers gave their defence or goalkeeper enough problems.
"If you allow players to do what they want and you don't get close to them and you don't stop them, they will cause you problems and they did that today."
Curle also accepted that Oliver's red card, as harsh as it was, had no bearing on the result given that it came when the Cobblers were already 3-0 down.
"At 3-0 the game is over," he added. "Some people might say we had a man sent off but that had no direct impact on the scoreline because the game was dead and buried before Vadaine got sent off."