Akhil Patel's century helped Northamptonshire to a solid first-innings total on the opening day of their Second XI Championship match against Sussex at Finedon.
Patel - who shone with the ball in Monday's one-day Trophy fixture against the same opponents - hit 118 in the County's 303 all out in 92 overs after opting to bat first.
Useful contributions also came from Zak Khawaja of Old Northamptonians (53) and Chad Barrett (56 not out).
Sussex had ten overs batting for the close and went in on 29 without loss.
The match resumes at Avenue Road on Wednesday.