The County seamer took took the third five-wicket haul in his last four innings before Sussex fought back on the first day of their LV=County Championship match.
Sanderson has 25 wickets this season - 15 of them against Sussex - after he took five for 45 in the home side's 175.
The 32-year-old took 10 wickets against Sussex earlier this month and his high-quality opening spell, when he took three for 17, helped reduce the hosts to 30 for four.
When Sanderson took his fourth wicket with the second ball after lunch Sussex were in dire straits on 67 for eight, but Jack Carson led a fightback with 52 - his maiden first-class half-century - as the last two wickets added 108.
Northants then reached 91 for four at stumps.
Sanderson said: "I don't know what it is about Sussex, but someone told me I'd taken 25 wickets against them in my last three games. Maybe they use wider bats and there are lots more nicks!
"The pitch is quite slow but a few nipped around this morning which wasn't surprising as I imagine the pitch had been under cover a lot because of all the rain we've had and we took some good catches in the slips, which are always the hardest to take.
"To be fair, they batted well in the afternoon but we also dropped a few catches which is disappointing because we could have nailed them for a really low score."
Sussex's Carson said: "There are three of us in the team who haven't played in front of a crowd before so even though it was only five or six hundred I was absolutely buzzing, especially when I got to my 50.
"I just wanted to take it all in, the applause of the crowd. It's the biggest crowd I've ever played in front of.
"We did a pretty good job to take four wickets and the pitch is doing as bit so we're still very much in the game."