Jim Mallinder admits Saints weren't smart enough as they failed to see out their game against Saracens at Stadium MK.
For the third match in succession, Mallinder's men conceded a late try and lost the match.
Marcelo Bosch's effort, allied with Alex Lozowski's successful conversion, saw Saracens snatch a 27-25 win in Milton Keynes.
And Mallinder, who had also seen his team suffer late heartache against Leicester and Wasps in recent weeks, was left to reflect on a third successive league defeat.
"There is a pattern in that we've played well and then lost it in the last few minutes," the Saints boss said.
"They've all been different games so there are different reasons for that.
"We will and need to keep looking at ourselves in terms of our game management, which clearly wasn't helped when Louis Picamoles and Stephen Myler aren't on the field (both were forced off injured).
"They are two of our key decision makers, but we've got some good players there and we probably could have been a little bit smarter at times."
Mallinder was irked by some decisions from referee Matthew Carley, with one second-half incident involving Ben Foden highlighted by the Saints boss.
"It was a nice break by Billy (Vunipola), he passed the ball, Fodes went to catch the ball, went up in the air and he was about to catch it when he got taken out," Mallinder said.
"It's pretty clear to be honest. I think everyone in the stadium saw it and I'm really surprised the ref had a look at the replay then stuck to his original decision.
"I'm sure the TMO wouldn't have asked him to look at it and put it on the big screen if he didn't think it had happened."
And Mallinder added: "For the third week in a row, we've played some good rugby, been ahead and it's really disappointing to lose in the last few minutes.
"It's a little bit of composure closing it out and a little bit of luck.
"Again, you look back at decisions and the Ben Foden incident was massive.
"Chris Ashton competed for the high ball and I'm convinced he touched the ball when it went into touch, and not our player.
"It's little things like that which make a big difference."