Exeter boss Rob Baxter accepted his Gallagher Premiership leaders deserved to lose as they fell to a 31-28 defeat at the hands of Saints at Franklin's Gardens on Friday night.
Santiago Cordero, Matt Kvesic and Ben Moon scored Exeter's tries, with Gareth Steenson converting all three.
There was also a penalty try awarded, but despite their pack dominating large periods, they came away with just two bonus points, thanks to Kvesic's last-minute try.
Dan Biggar racked up 16 points for Saints with a try, a penalty and four conversions, with further scores coming from Cobus Reinach, Fraser Dingwall and Piers Francis.
Baxter, who had seen his side beat title rivals Saracens at Sandy Park on the previous weekend, said: "I thought Northampton thoroughly deserved the win.
"They turned up in a better frame of mind, with better physicality and better commitment to the game than we did.
"We did fight our way back into it and our forwards got some dominance, particularly at the scrum area.
"We did get four tries away from home and picked up two points away from home, but it was all about Northampton. They played better than us.
"We've got to have a bit of a look at ourselves and perhaps decide that sometimes a Christmas party after beating Saracens potentially isn't the best way to prepare for a game away against a team that is going to come out and fight.
"I've said to the lads that they need to get their heads around it because another team will come out fighting against us next week.
"It's not just about going out on the field, knocking games over and winning.
"You win games because of the commitment you put in to doing what we do.
"There was some pretty poor play for us."