U.S. international Aron Johannsson scored the winner to lead AZ Alkmaar to a 1-0 win at Ajax on Thursday.
Ajax's second defeat in a week leaves their pursuit of a fifth consecutive Eredivisie title in disarray. Frank de Boer's team are 12 points behind leader PSV Eindhoven.
The hosts were reduced to 10 men in the 62nd minute when Niklas Moisander was sent off for pushing striker Johannsson while he was in a goal-scoring position.
Johannsson was not to be denied, and scored the winner 14 minutes...