Striker Kolbeinn Sightorsson broke the deadlock eight minutes before the interval with his first goal for champions Ajax though seconds later Heerenveen's Viktor Elm set up Bas Dost for the equaliser.
Toby Alderweireld restored the lead for the home side before the break with a 30-metre drive, while Derk Boerrigter, Miralem Sulejmani (pictured) and Gregory van der Wiel completed the rout in the second half.
After two matches and two wins, Ajax are top on goal difference from arch rivals Feyenoord, who beat Roda JC Kerkrade 3-0 on Saturday.
Twente Enschede, 2-0 winners against AZ Alkmaar on Saturday, are third also with maximum points.
Heracles Almelo came from behind to beat NAC Breda 2-1 while Utrecht fought back for a 2-2 draw against Graafschap Doetinchem, who enjoyed a two-goal lead after goals from Rydell Poepon and Soufian El Hassnaoui.
