Auckland lost their lead in the domestic 50-over competition when well beaten by Central Districts at Eden Park yesterday.
Having sent CD in, Auckland found themselves seeking 304 which would have kept them top after four rounds.
CD's opener Jamie How hit 156 off 139 balls, sharing a second-wicket record stand against Auckland of 142 with Dane Cleaver, who made 60.
Auckland's response never really got going. They lost five for 47 at one point and were dismissed at 190 for a 113-run defeat. Only Anaru Kitchen, with 59, and tailender Matt Quinn, who hit 36, passed 30.
Northern Districts went top with a tight three-wicket win over Wellington in the capital.