Jake Libby hit 102, whilst Rory Kleinveldt scored a blistering 97, as the Northamptonshire batsmen enjoyed a good day despite three wickets for Shiv Thakor.
Thakor returned 3-65 with all three coming during a fantastic afternoon spell in which Derbyshire looked to gain control by taking four wickets for just 17 runs.
The hosts’ batsmen had other ideas though, as Kleinveldt played some extravagant shots to score 97 off 69 balls during a 140-run partnership with Richard Levi who ended the day on 84 not out with Northamptonshire 438-7, leading by 114 runs.
Having begun the day on 66-0, overnight batsmen Libby and Ben Duckett were able to defy some tight bowling by Derbyshire to put on a century opening stand.
The stand was broken on 109 when Andy Carter enticed Duckett into an edge on 60, which sailed to Wes Durston in the slips.
Alex Wakely joined Libby at three and the pair batted slowly either side of the lunch break until Wakely missed a straight one from Thakor and was out lbw for 35. Soon after, Thakor had Josh Cobb out too as he was caught by Neil Broom at mid-wicket without scoring.
Meanwhile, Libby had managed to keep his wicket in tact and moved through to his first century for Northamptonshire and the second of his first-class career. He was out soon after though as Durston trapped him lbw on 102.
Thakor then bowled Steven Crook for one to take his third wicket in 15 balls as the hosts went from 191-1 to 208-5 in the space of six overs.
Derbyshire had taken the initiative but it was soon stolen away from them as Levi and Kleinveldt set about creating an explosive seventh wicket partnership.
Kleinveldt reached his half-century from just 20 balls whilst Levi took 63 balls to reach the same milestone as the two put on over 100 in blistering time.
Kleinveldt looked set for a stunning century until, on 97, he attempted to reach his century with a big shot and was caught by Hamish Rutherford on the leg-side boundary off Tony Palladino.
Levi did manage to reach the close without falling though, ending Day Three unbeaten on 84, alongside Graeme White who was 23 not out in the hosts’ 438-7.
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