Derbyshire 374 for 5 (du Plooy 159*, Madsen 143) lead Worcestershire 237 by 137 runs
The duo scored centuries and broke a 31-year-old landmark in establishing a new Derbyshire record of 267 from 70 overs for the fourth wicket against the home side. They went past the previous best partnership of 218 by Peter Bowler and Chris Adams at Derby in 1992.
Madsen has always enjoyed batting against Worcestershire and in 24 innings has struck four centuries and nine other fifty plus scores.
Their efforts have given bottom-placed Derbyshire a realistic chance of completing a first win in 10 Championship matches since they triumphed in the corresponding fixture last season.
They will begin day three with a lead of 137 and five wickets in hand and du Plooy unbeaten on 159. But they were aided by an uninspired performance by the home side who dropped both of the batters before they reached three figures.
Du Plooy was put down on 69 off Indian pace bowler Navvdeep Saini, a sharp chance to Ed Pollock’s left at slip. And Pollock also spilled a more straightforward chest-high opportunity offered by Madsen on 94 against Leach.
Leach was head and shoulders above the rest of the Worcestershire attack and he made the only breakthrough with the ball during the opening two sessions.
Worcestershire were guilty of bowling too many ‘four’ balls during the first part of the day to hand Derbyshire a momentum they never relinquished and their ground fielding was also below-par.
Derbyshire resumed on 32 for 2 and Leach made a further breakthrough with the fourth ball of the day. Brooke Guest did not move his feet to a delivery which nibbled away as he edged through to keeper Gareth Roderick.
It was Leach’s 33rd scalp of the season and he asked questions of both batters during a typically probing opening spell.
But Indian pace bowler Saini initially found it hard to find the right line and length on his debut He was driven for a succession of boundaries by Madsen and du Plooy and Dillon Pennington also leaked runs during his initial spell and the fourth wicket pair looked untroubled against the Kookaburra ball on a slow pitch.
Matthew Waite had a moral victory when du Plooy edged the allrounder for four. But Derbyshire scored freely and Madsen’s 56 ball half century contained 11 boundaries.
The 100 partnership was completed in only 19.1 overs and du Plooy followed Madsen to his fifty from 68 deliveries with 10 fours. The morning session produced 126 runs off 28 overs.
Saini bowled with plenty of pace and aggression in the post lunch spell and should have had picked up the wicket of du Plooy on 69 but Pollock spilled the chance at slip away to his left.
Leach replaced the Indian pace bowler and Madsen on 94 edged him at chest height to Pollock who again spilled the opportunity and immediately left the field clutching his finger.
Madsen completed his fourth hundred against Worcestershire off 148 balls with one six and 16 fours and du Plooy followed him to three figures from 144 deliveries with 14 boundaries.
The first delivery with the second new ball finally broke the partnership when Madsen was lbw to Leach for 143 and then Haider Ali tried to cut Pennington and feathered through to Roderick. But du Plooy went onto complete his 150 from 249 balls with one six and 19 fours before the close.