In the first part of the Edgbaston Midlands double-header, Falcons took bragging rights against the Foxes by successfully chasing down a target of 197.
Leicestershire opener Sol Budinger bludgeoned 49 from 24 deliveries to set the platform as his team looked to set an imposing target for bottom side Derbyshire.
When Budinger was dismissed by veteran spin bowler Samit Patel (2-33), the Foxes had rapidly moved to 65-2 in the early stages of the eighth over.
Rehan Ahmed and Shan Masood were dismissed in quick succession by Falcons seamer Pat Brown, who finished with 3-51, but Logan van Beek (26 not out) and Ben Cox (28 not out) put on 55 in the final five overs to hand Derbyshire a tough chase.
In reply, Derbyshire opener Donald continued where he left off following Friday's knock of 73 not out against Nottinghamshire with a terrific 60 to help them race to 80-0 after six overs.
That included the fastest half-century in the club's history from just 18 balls - beating his own previous record set in last year's competition.
Leicestershire were given a glimmer of hope when seamer Tom Scriven removed both openers in his first over.
And when Wayne Madsen found Matt Salisbury at deep fine leg for Scriven's third wicket, Derbyshire were still 43 runs shy of their target with 32 balls remaining.
But a terrific 52 not out in just 32 balls from 40-year-old Patel, accompanied ably by Ross Whiteley (13 not out), helped the Falcons home comfortably with 10 balls to spare to seal back-to-back victories in consecutive days.