Siem de Jong scored a hat trick as Ajax beat Heerenveen 5-0 to take a three-point lead at the top of the Eredivisie.
Theo Janssen and Ismail Aissati also netted for the defending champions, who are three points ahead of AZ with five rounds remaining.
AZ had led the standings for much of the season but were held to a 2-2 draw at Steve McClaren's Twente. American forward Jozy Altidore scored twice for AZ, but Luuk de Jong and Emir Bajrami replied for Twente.
PSV dropped to fifth after losing 2-1 at RKC Waalwijk, with Sander Duits and Mitchell Schet scoring in a two-minute span in the second half. Jan Vennegoor of Hesselink replying in the 86th for PSV.