Rookies Steffan Piolet and Paul Best swept Warwickshire to the top of Group C of the Clydesdale Bank 40 with an unexpected three-wicket victory under the Edgbaston floodlights under the Duckworth-Lewis Method that effectively dashed Yorkshire's already slim semi-final hopes.
Piolet, who batted with a runner after he sustained a hamstring injury bowling, and Best added 40 in just three overs to take Warwickshire to a revised target of 238 in 34 overs with four balls to spare.
Yorkshire thought they had the match won when Tim Ambrose, who made a bustling 64 from 47 balls, carved Moin Ashraf to short third man. But Piolet turned the match decisively in Warwickshire's favour when he pulled Steven Patterson and Ashraf for sixes in consecutive overs to finish unbeaten on 23 from nine balls.
Best followed up his competition-best bowling of three for 43 with a rapid unbeaten 16, also from nine balls, to take Warwickshire above Sussex in the group.
Yorkshire will wonder how they contrived to lose their fourth game in the competition this season after captain Andrew Gale (76) and Adam Lyth (69) laid the foundations for a competitive total with aggressive half-centuries.
But Yorkshire lost five quick wickets after they returned to face 19 balls after a 65-minute stoppage for rain and Warwickshire's run chase was sustained by a third-wicket stand of 74 in 10 overs between Ambrose and captain Jim Troughton.
Neither could finish the job, as Troughton was bowled for 61 driving at Azeem Rafiq and Ambrose fell when victory was in sight, but Piolet and Best, who have become one-day regulars this season, proved their worth.
Defeat was particularly hard on Lyth, who played a superb attacking innings which included four sixes in six balls, three of them off consecutive deliveries from Chris Wright either side of the rain break. The second of those took Lyth to a 49-ball half-century and he added a fourth off Keith Barker before he skied the next ball to mid-wicket.
Warwickshire's run chase was interrupted by some brilliant fielding by South African David Miller, who held two catches including a superb running effort at deep mid-wicket to account for William Porterfield, and was also involved in two run-outs.
But Yorkshire's bowling under pressure was not quite so assured, with Warwickshire successfully chasing down 83 from the last 10 overs.