Nottinghamshire blasted 294-8 - their highest-ever score in 40-over cricket - to defeat Durham by 43 runs in the Clydesdale Bank 40 at Trent Bridge.
Both sides were all but out of the semi-final places in Group B before the match started.
But ICC World Twenty20 winner Michael Lumb looked like he had a point to prove ahead of the announcement of England's final 15-man squad to defend their title in Sri Lanka.
The left-hander hit three fours off the fourth over, delivered by Ben Stokes,
and launched Chris Rushworth and Mitch Claydon for six as he raced to 50 off 31 balls.
The opener had hit a blistering 84 off 51 balls, including 14 fours and two sixes, when he was bowled by Claydon.
But Riki Wessels kept up the momentum with 43 from 28 balls, hitting three sixes and four fours, while a terrific late assault from skipper Chris Read, who hit an unbeaten 71, boosted the score once more.
Despite the in-form Mark Stoneman hitting his second successive century in the competition, Durham were unable to keep up with the hefty run-rate required and were bowled out for 251.
Fast bowler Andy Carter claimed 4-45 - his best figures in List-A cricket for Nottinghamshire - while medium-pacer Steven Mullaney accounted for Stoneman for 102, Paul Collingwood and Dale Benkenstein to finish with 3-44.