Chesney Hughes scored his first hundred for two years and shared a double century opening stand to put Derbyshire in a strong position against Northamptonshire.
Hughes and Ben Slater dominated the first two sessions on the third day at Derby, by adding 205 in 77 overs.
And at tea, the home side are 281 for 3, with a lead of 300.
It was Hughes’s first century since his 270 against Yorkshire at Headingly in May 2013 and his celebrations showed what it meant.
Although he was perilously close to being run out when he scampered through for the single that took him to three figures off 249 balls.
The Anguillan was lbw to Rob Keogh for 104 but Slater missed out on a century when he was caught behind for 96 cutting at David Willey who bowled Hashim Amla for 20.
But Derbyshire are well placed to push for victory.