Sussex captain Ben Brown was made to regret his decision to bat first at Wantage Road as Northamptonshire reduced the visitors to 90-7 at lunch on day one of the final game of the season.
After losing Phil Salt caught at slip off Brett Hutton for 20, Sussex steadied to 58-1 before Luke Wells shouldered arms to Ben Cotton and lost his off stump to one that swung back.
From there, Northants chipped away regularly as Nathan Buck brought one back to bowl Harry Finch second ball for a duck and Michael Burgess tamely chipped Cotton to short midwicket.
At 78-4, Northants were on top but they took three more wickets before the break. Ben Sanderson nipped one back to beat Laurie Evans drive to remove his off stump for a smartly-compiled 34 before Delray Rawlings edged his first ball to Ricardo Vasconelos at slip.
Chris Jordan survived the hat-trick ball but fell lbw to Hutton at the start of the next over.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here