Derbyshire claimed their first LV= County Championship win of the season by easing to a nine-wicket triumph over title challengers Sussex with 11 overs to spare on day three.
It was a potentially fatal blow to Sussex's hopes of winning their fourth title since 2003. They have not won a home championship match for a year and were always up against it after being dismissed for 133 in their second innings, with Tim Groenewald taking 5- 40.
That left Derbyshire needing 174 for victory and they got there in 42.3 overs thanks to an unbroken stand of 102 between skipper Wayne Madsen and opener Ben Slater, who both made unbeaten half-centuries.
Sussex resumed on 11 for one - a lead of 51 - but the rot set in after they lost a second wicket to the third ball of the day, Luke Wells edging Groenewald to Peter Burgoyne at third slip.
Michael Yardy was third out in the 11th over when he edged a sharply bouncing delivery from Mark Footitt behind. Nightwatchman Lewis Hatchett then shuffled across his stumps to be lbw to Groenewald and make it 22 for four.
When Rory Hamilton-Brown was fifth out seven runs later, lbw to a Footitt yorker, Sussex had lost four wickets for 18 runs in 7.3 overs.
Captain Ed Joyce, their saviour on a number of occasions this year, looked in the mood for another rescue act before falling leg before to Matt Higginbottom for 17, although he appeared unhappy with the decision.
That left Sussex 62 for six and recovery was beyond them. Ben Brown pushed forward and edged Alex Hughes to first slip, while Luke Wright, who scored a vigorous 49 from 75 balls with nine fours, drove at a wide delivery from Groenewald after lunch to be caught behind and leave the score on 124 for eight.
Steve Magoffin missed a straight one, falling lbw to Footitt, and the innings ended when Chris Jordan, who made 23 and had done his best to shield last man Monty Panesar from the strike, attempted to pull a short delivery from Groenewald and lost his leg stump.
When Derbyshire batted again, they were given a positive start by Slater and Chesney Hughes, who put on 69 before the latter was bowled for 34 as he played no stroke to Jordan, his 51st wicket of the season.
But Slater went on to score a maiden championship fifty from 94 balls, with seven fours, and was well supported by his captain, whose undefeated 62 was his second half-century of the match.