New Zealand opener Martin Guptill turned on the style as Derbyshire crushed Yorkshire by six wickets in the Clydesdale Bank 40.
Guptill scored an unbeaten 103 off 83 balls as the Falcons flew past Yorkshire's total of 234-7 with 38 balls to spare.
Gary Ballance scored an unbeaten 81 off 65 balls and Jacques Rudolph made 75 for the visitors.
But Guptill smashed four sixes to give the home side a convincing victory in front of a 3,000-plus crowd in Chesterfield.
Yorkshire raced to 56 off the first eight overs but once Derbyshire took the pace off the ball the run rate dropped and wickets started to fall.
Rudolph hit seven fours on his way to a 46-ball 50 before he was stumped and when Gerard Brophy skied to mid-off in the 34th over Yorkshire were struggling to post a competitive total.
But Ballance changed that with a thrilling onslaught that broke Derbyshire's stranglehold.
Yorkshire posted a decent total after piling on 52 runs in the last four overs - although Guptill soon made it look inadequate.
He drove and pulled Oliver Hannon-Dalby for two sixes and cut David Wainwright for his sixth four to reach 50 off only 34 balls.
Steve Patterson gave Yorkshire hope with two wickets in successive overs but Guptill secured his century before hitting the winning single.