Cobblers boss Jimmy Floyd Hasselbaink labelled his side's performance against Gillingham on Tuesday as 'just not good enough' and conceded it was in the first half when the game was lost.
Dominant from the word go, Josh Parker blasted Gillingham into a sixth-minute lead at Sixfields before Tom Eaves poked in Luke O'Neill's low cross to make it 2-0 with just 18 minutes on the clock.
The visitors could have added more by the time Cobblers skipper Ash Taylor reduced the arrears with a second-half header but there was to be no way back for the home side, who also had Hildeberto Pereira sent off after the final whistle.
"The first-half is where it went wrong," said Hasselbaink. "We just didn't look like playing football whatsoever and it was very easy for them to get in behind us with simple long balls.
"We couldn't deal with their long balls and it was as direct as that. I don't know why but it's a big disappointment for me, especially after the Saturday game.
"We took a lot of steps forward at the weekend and, after the Rochdale home game, we wanted to put things right but to have a performance like that is just not good enough."
After admitting to dishing out some choice words at the break, Hasselbaink's team were vastly improved in the second period but it still wasn't good enough as Gillingham followed in the footsteps of Rochdale in coming away from Sixfields with three deserved points.
Hasselbaink added: "We didn't create as many chances as we wanted to after scoring the goal.
"Everything was a little bit too rushed and we didn't stay calm enough and weren't patient enough.
"We had a few moments but they weren't clear-cut moments where we should have scored. We were the better team in the second-half and it was a lot better although we couldn't have got much worse.
"The second-half was 10 times better but we weren't calm and patient with our passing.
"Harsh words were said at half-time but that's normal. We needed a reaction, a positive reaction, and we got that but we didn't continue it and that was disappointing.
"We could have done with at least a draw today and it would have been positive result after being 2-0 down."