Durham's hopes of reaching the Yorkshire Bank 40 semi-finals were all but ended when Derbyshire skipper Wayne Madsen inspired his team to a crushing 107-run victory in Group B under the County Ground floodlights.
Madsen made 37 and shared a century stand with Richard Johnson (58) as Derbyshire made 217 for eight before he ambushed Durham with his off-spin to take three for 27 - his best figures in any form of cricket - as the visitors collapsed on a slow, turning Derby pitch.
Durham never recovered after Madsen reduced them to 62 for four and David Wainwright took a limited-overs career-best four for 11 to send the visitors crashing to 110 all out in the 29th over as Derbyshire ended a run of four defeats to Durham this season.
The Dynamos had to win and started well against a weakened Derbyshire team missing Shivnarine Chanderpaul and Wes Durston, leaving their hosts in trouble on 36 for three in the ninth over.
Mark Wood nibbled one away to have Ben Slater caught behind for six in the fourth over and after Chesney Hughes pulled Wood for six, he tried to repeat the shot against Chris Rushworth and holed out to deep midwicket for 24.
Derbyshire were struggling when Wood had Paul Borrington caught at gully but Madsen joined Johnson in a stand that put the Falcons back in the match.
Johnson had a lucky escape when he was caught behind for 17 with the total on 61, but Ben Stokes had overstepped and that proved costly as the fourth-wicket pair worked the ball around to add 103 from 114 balls.
Madsen straight drove Gareth Breese for six and Johnson hit four fours in a 58-ball 50 before Paul Collingwood switched ends to remove them both in the 27th over.
Madsen mistimed a pull and was caught at mid on and three balls later, Collingwood cut one back to bowl Johnson but 22 from 15 balls by Tony Palladino and 25 extras lifted Derbyshire to a challenging total.
It looked an even better one when Madsen opened with his occasional off-breaks and struck twice in a five-over spell that cost only 13 runs.
Phil Mustard tried to cut a straight one and was bowled for a duck and Scott Borthwick pulled to deep midwicket to put Durham on the back foot at 14 for two.
Collingwood and Mark Stoneman added 46 in nine overs, but it was not easy to force the pace and when Madsen returned at the Grandstand End, Stoneman was caught at long off for 25 when he tried to hit down the ground.
It was impossible to keep Madsen out of the game and he took a simple catch in the next over when Collingwood pushed Tom Knight’s left-arm spin to short extra cover.
Knight struck another huge blow when he bowled Stokes for nine and celebrated his best List A figures of three for 36 before Wainwright sealed victory with 11.4 overs remaining.