Rob Baxter admits Exeter have some reasons to fear Saints as the teams prepare for a rapid reunion next Saturday.
The Chiefs scored 19 unanswered second-half points yesterday to secure a 40-21 Gallagher Premiership victory against Chris Boyd's side.
But it didn't damage Saints' chances of finishing fourth as Wasps did them a favour by beating Harlequins 27-25 at the Ricoh Arena.
And the black, green and gold will now head back to Sandy Park next weekend as they bid to secure a play-off semi-final win and book a place in the grand final at Twickenham on June 1.
Exeter finished the regular season top of the table, with Saracens second and Gloucester third.
And Chiefs boss Baxter said: "I thought the second half performance was fantastic from us.
"The way the guys rolled up their sleeves and kind of decided the game was going to go our way was fantastic.
"Are there things that worry me? Definitely. The speed of some of Northampton's scores, particularly on the counter-attack, is something we need to look at.
"There was a little bit of rustiness around the first half but we worked our way through that, and we did it under a lot of pressure from Northampton.
"We grew in strength as the game went on, which is what I wanted to see.
"Double-headers are hard situations to deal with as a player and a coach, and we have to make sure mentally we are bang-on on Monday.
"The job is far from done.
"Northampton are a very dangerous side, and we are going to have to be prepared to work at least as hard again next week - if not harder - if we want to get to the final."