Jim Mallinder admits Saints will be left with regrets after failing to close out their game against Leicester Tigers at Franklin's Gardens on Saturday afternoon.
Mallinder's men had led 22-16 at half-time thanks to tries from Nafi Tuitavake, Ahsee Tuala and Louis Picamoles.
Saints thought they had the bonus point before the break, but Christian Day's foot was deemed to be in touch as he dived over in the corner in the final play of the half.
But the home side were still in control with 12 minutes to go, when Tigers flanker Mike Williams was sin-binned for a challenge on Teimana Harrison at the breakdown.
Saints were 28-23 up and Stephen Myler had a penalty chance, but he missed and Leicester recovered to score with 14 men and then seal the win with an Owen Williams conversion and two penalties.
"It could have gone either way," Mallinder said.
"We made a very promising start, there were a few key moments in that game where as we watch it back we'll think 'what if?'.
"Particularly at the end of the first half, we had a very good overlap and should have scored that.
"There were a few other interesting incidents, but it was a close game, either side could have won it and unfortunately we didn't win it today."
Saints struggled to get decisions at the scrum, with referee Greg Garner penalising them five times to Tigers' none.
And Mallinder said: "The referee thought our scrum was a bit of a problem so we got penalised on a few occasions there, which made it difficult.
"But generally we attacked well, with really good focus and intensity, and we scored some good tries.
"We will need to have a good look at the scrum and when the penalties are against you like that, you're always up against it.
"Even that last penalty gave them a lead and if they hadn't got that, we'd have got a penalty and wouldn't have to tap and go. We'd have kicked it and won the game.
"They were very crucial decisions."