An extraordinary innings of 97 in 69 balls from Rory Kleinveldt put Northants in charge against Derbyshire at Wantage Road.
The home side closed day three of the County Championship Division Two clash on 438 for seven, which is a lead of 114.
Kleinveldt’s blasting began straight after tea and a combination of efficient driving through the covers and well-timed flicking over the leg side saw him race to a half-century in just 20 balls. Andy Carter bore most of the damage with 24 coming from the 89th over.
The field went back and Kleinveldt picked off more singles and punished the occasional loose delivery - the worst of them a rank long-hop from Wes Durston that was smashed over deep midwicket for Kleinveldt’s third six.
But three away from just a second first-class century, Kleinveldt aimed at the short Clarke Road boundary, mistimed a flick, and found Hamish Rutherford running in to give Tony Palladino a first wicket. Kleinveldt peeled himself from the wicket.
His partner, Richard Levi, will hope to bring up a first century of the season on day four, going to the close 84 not out.
It was the majority contribution to a stand of 140 for the seventh wicket with Levi in just 19.5 overs. It blew away the pressure Derbyshire had built up shortly before tea.
Shiv Thakor took three wickets in 15 balls to put Derbyshire on top and at the second interval, Northants were 254 for six, trailing by 70.
Earlier, at 191 for one, the hosts were making serene progress with Jake Libby having brought up a second first-class century - and first for Northants - in 217 balls with 13 fours.
But he was the third of four wickets to fall for just 17 runs, trying to leave Durston’s off spin and given out lbw for 102.
The collapse began when Alex Wakely played across his front pad to be lbw for 35 - Thakor’s first wicket - before Josh Cobb clipped the same bowler to short-midwicket, out for an 11-ball duck, and Steven Crook lost his middle stump for 1.
And in the over before tea, Adam Rossington guided Luke Fletcher towards gully, where Durston took to sharp catch diving to his left for Derbyshire’s second bowling bonus point.
It was a remarkable turnaround after the majority of the day saw Derbyshire struggling to create chances and Ben Duckett in good form. He brought up a third fifty of the season in 87 balls with nine fours. He was the only wicket to fall before lunch after an opening stand of 109.
Carter, in his first over of the day, conceded two boundaries to Duckett before having him caught at second slip for 60.