Ajax had the points sewn up by half-time as Niklas Moisander put them ahead after 22 minutes and Christian Eriksen doubled the lead five minutes before the break.
Feyenoord went down to a shock 3-2 defeat at PEC Zwolle, who moved out of the bottom three.
A Graziano Pelle own goal after two minutes gave the hosts the perfect start and Darryl Lachman added a second just five minutes later.
Pelle made amends by scoring twice in two minutes to bring the game level before the break, but Denni Avdic grabbed the winner for PEC with 15 minutes to go.
Defeat left the Rotterdammers in fourth place, six points off top spot.
Vitesse Arnhem beat FC Groningen 2-0 thanks to goals from Mike Havenaar (53) and Wilfried Bony (63) with a penalty.
Heerenveen defender Joey van den Berg had a day to forget as he scored an own goal and was sent off in the first half of his side's 2-1 loss at ADO Den Haag.
Van den Berg's 24th-minute own goal cancelled out Sven Kums' 13th-minute opener and ADO completed the comeback when Santi Kolk put them ahead in the 36th minute.
Van den Berg was dismissed a minute before the break and his side could not mount a second-half fightback.