Alan Dickens was 'bitterly disapppointed' after Saints suffered another defeat at Franklin's Gardens.
Exeter Chiefs claimed a 35-14 success, inflicting a sixth successive league loss on Northampton, who have lost 11 of their past 12 matches in all competitions.
Saints had shown spirit in the first half of the sold-out clash at Franklin's Gardens, fighting back from 8-0 down to go in at 11-7 behind at the break.
Ahsee Tuala got the try for the home side, but that was as good as it got as Exeter turned up the power in the second period, scoring three further tries to bag a bonus point.
Cobus Reinach claimed a late second score for Saints, but it was scant consolation on another frustrating afternoon.
"I'm bitterly disappointed after the effort the lads have shown this week and in the first 50, 60 minutes," said Dickens, who is in interim charge following the departure of Jim Mallinder.
"We didn't get the rewards.
"We didn't get enough possession and when we did get it, we didn't look after the ball and that cost us against an Exeter team who were able to keep the ball for long periods of time.
"Ultimately, we gave away 22 penalties and only got eight. Read into that what you will.
"The crowd certainly voiced their disapproval at some of the decisions and I understand that frustration.
"It gave Exeter field position and they were able to squeeze us.
"They're the team in the league that keep the ball for the longest period of time and when we got it, we didn't look after it."