Alan Gaffney admitted Saints went back to bad habits in their crushing 62-14 defeat to Saracens at Allianz Park.
The black, green and gold shipped seven tries, making it 24 conceded in three meetings with Saracens this season.
The aggregate score is 174-51 in the Barnet-based side's favour, with Saints out of Europe after suffering five defeats from six Champions Cup matches this season.
They had started brightly at Allianz Park, with Cobus Reinach and Nafi Tuitavake scoring for a team buoyed by back-to-back wins against Gloucester and Clermont Auvergne.
But once Saracens got a grip of the game, Saints struggled to deal with them and it was another sobering afternoon for the away side.
"We've got to get a totally different mindset when we come out and play these games - we've got to step up," said Gaffney, who suffered a first defeat since being appointed Saints coaching consultant at the start of the year..
"We can't take a backward step, which is what we did through most of the game today.
"It's quite amazing that we only conceded two tries in the second half because it was total domination by them.
"They had all the ball and the stats won't be good.
"When we played on Sarries, we made some inroads, but when we tried to play out the back and off them, we're just not good at that.
"We've got to back our skill level and be aggressive.
"We've been better in the past couple of weeks, but we can't sit back on the line and wait for sides to come at us.
"Sometimes when the pressure comes, people revert to bad habits and we've all got to front up on Monday now."