Durham Dynamos’ hopes of reaching the Yorkshire Bank 40 semi-finals were all but ended when Wayne Madsen inspired Derbyshire Falcons 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, who hit 58, as Derbyshire made 217 for eight.
He then ambushed Durham with his off-spin to take 3-27 - 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-best 4-11 to send the visitors crashing to 110 all out in the 29th over as Derbyshire ended a run of four defeats to the north-east county 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 as Ben Stokes had overstepped. 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 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.
However, 22 from 15 balls by Tony Palladino and 25 extras lifted Derbyshire to a challenging total on a slow pitch.
It looked even better when Madsen surprisingly 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, while Scott Borthwick pulled to deep midwicket, putting 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, the latter was caught at long-off for 25.
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 the dangerous Stokes for nine and celebrated his best List A figures of 3-36 before Wainwright sealed victory with 11.4 overs remaining.