Jim Mallinder admits Saints are 'in a hole' after suffering their fifth successive Aviva Premiership defeat.
Nili Latu scored a last-gasp try and Sonatane Takulua kicked the conversion to earn Newcastle Falcons a dramatic 24-22 victory at Franklin's Gardens.
It left Saints stunned as they had looked set to triumph after Harry Mallinder's first-half effort, a penalty try and a score from Dylan Hartley put them in control.
The Falcons, who had gone 14-5 up thanks to tries from Sinoti Sinoti and Josh Matavesi, kept fighting as they ended their four-match league losing streak.
And Saints boss Mallinder said: "It was a scrappy first half, scrappy from both sides.
"We got turned over too many times, not getting enough numbers to the breakdown and we conceded a couple of loose tries.
"We dominated in the second half, creating pressure, playing pretty well and we just couldn't score.
"Then to concede in that final minute was really heartbreaking.
"We had a chance to win at Sale last week, but we couldn't score late on and lost the game.
"We've lost late on again today and it's really hard to take."
Saints have now lost eight of their past nine matches in all competitions, with their only win coming against the lowly Dragons in the Anglo-Welsh Cup.
Pressure continues to mount on everyone at the club.
And Mallinder said: "We needed to turn the corner today and we haven't done it, so we are in a hole, we're admitting that.
"We've got to start climbing up that hole and get out of it."