In the Yorkshire Bank 40, a fighting 96 at Headingley from Group C leaders Gloucestershire's Australian captain, Michael Klinger, condemned Yorkshire to a five-wicket defeat.
Paul Stirling hit a superb unbeaten 132 off 96 balls as Middlesex defeated Leicestershire by 10 wickets. Somerset bounced back to winning ways when they beat Glamorgan by three wickets with 10 balls to spare.
In Group A, a maiden one-day century by Northamptonshire captain Alex Wakely spearheaded a 29-run win against Kent.
In Group B, Durham clinched a 39-run win over Lancashire at Chester-le-Street.
Ryan ten Doeschate blazed 180 off only 98 balls to lead Essex to victory over Scotland at Chelmsford.