Having dismissed the hosts for 230 inside 83 overs, Alex Wakely’s side survived fading light to go in at stumps on 31 without loss, having cut Kent’s overall lead to 199 going into day two.
Batting first, after Northants elected to field, Kent were dismissed soon after 5pm as half-centuries by Sean Dickson, Will Gidman and Matt Coles helped them to bank their sole batting bonus point.
Openers Dickson and Daniel Bell-Drummond made watchful starts as Northants’ new-ball pairing of Rory Kleinveldt and Ben Sanderson extracted swing in the humid conditions and tennis-ball bounce from the pitch.
With his score on 20, Bell-Drummond fenced at a lifting leg-cutter from Sanderson and edged to the diving David Murphy to make it 59 for one.
One delivery before the scheduled lunch break, Joe Denly mistimed an attempted hook shot against Steven Crook to be caught behind off the toe end of the bat.
Having tended to bowl too short in the opening session, Northants’ seamers pitched the ball up a little more after lunch and Muhammad Azharullah was rewarded with two wickets in as many balls.
Sam Northeast (9) pushed at one that swung in late and held its line to the graze the outside edge for Murphy’s third catch, then Darren Stevens, defending on the line of off stump, nicked similar delivery low to Rob Keogh at second slip.
Dickson’s patient 50 from 121 balls sparked the introduction of spin for the first time in the match with Keogh sending down the 50th over. The move paid immediate dividends when Dickson, on 63, miscued to mid-on.
Stand-in keeper Callum Jackson recorded the third duck of Kent’s innings when he sliced an ambitious drive to substitute fielder Saif Zaib at backward point.
Kent’s gloom deepened soon after tea when James Tredwell, aiming a leg-side clip across the line of a Kleinveldt in-swinger, went lbw for 12.
Gidman and Coles combined nicely for the eighth wicket, with Coles hoisting Keogh over long-on for the first six of the match.
In trying to repeat the blow three balls later, the burly all-rounder miscued to mid-on where Sanderson dropped a comfortable overhead catch, with Coles on 25.
Gidman recorded his fourth successive championship half-century since joining on-loan from Nottinghamshire from 95 balls, but trooped off unhappily moments later after picking out Kleinveldt with a leg-side clip.
Coles mixed the spectacular with the incomprehensible; reverse pulling Keogh for meaty a six, he then heaved at the same bowler to see the ball bounce over his stumps off a bottom edge for a couple of fortuitous runs.
His 41-ball 50 came with another slice of luck when Azharullah downed a diving chance at mid-on, but the second new ball in the hands of Kleinveldt ended Coles’ fun when he steered to second slip to see Richard Levi grasp a throat-high chance.
Kleinveldt polished off Kent’s innings in his next over by having Hardus Viljoen caught by White at third slip. Kleinveldt finished with three for 70 while Crook and Azharullah bagged two wickets apiece.
Ben Duckett then made his way to 19 not out and fellow opener Rob Newton made eight not out before the first day was brought to a close.