After the White Rose county had been dismissed for 249 just before the close yesterday, Northants started brightly courtesy of some fine hitting from Stephen Peters and Kyle Coetzer.
They raced past the 50 mark inside 14 overs and seemed set to build a commanding innings when Azeem Rafiq made the breakthrough.
Coetzer was the man to go for 31, the opener attempting to cut the spinner but only managing to find the safe hands of Phil Jaques at gulley.
The dismissal, which came with Northants on 66, was then followed by Yorkshire claiming a second wicket just before the interval as David Sales edged Richard Pyrah to Adam Lyth at second slip.
Stephen Peters, whose unbeaten 45 came from 90 deliveries, and Alex Wakely ensured the home side reached lunch without further loss to leave the game finely balanced.