PSV had won four and drawn three of their opening seven matches but came unstuck on Saturday as goals from Nick Viergever (21) and Aron Johannsson (57) saw AZ collect the three points.
Memphis Depay hit a 35th-minute reply for PSV, who are now only narrowly ahead of Ajax after the Amsterdammers cantered to a 6-0 win at home to promoted Go Ahead Eagles.
Ajax desperately needed a response after their 4-0 mauling at the hands of PSV a week ago - a result which followed a loss by the same scoreline at the hands of Barcelona in the Champions League - and duly delivered a morale-boosting performance.
The hosts were kept at bay in the first half but the floodgates opened after the break, triggered by a 48th-minute Jop van der Linden own goal. Lesley De Sa made it two in the 50th minute while Kolbeinn Sigthorsson's quickfire brace complete a spell of four goals in five minutes.
It was 5-0 when Lerin Duarte fired home in the 64th minute while Siem De Jong completed the scoring with 21 mintues remaining as Ajax moved into second place, level on 14 points with PEC Zwolle, who were held to a 0-0 draw at home to NAC Breda.
FC Utrecht and Roda JC played out an entertaining 3-3 draw.
Cedric Van der Gun opened the scoring for Utrecht after 13 minutes but that was cancelled out by Krisztian Nemeth (28).
A Filip Kurto own goal restored the home side's lead but again Roda hit back, Mark-Jan Fledderus with the strike after 62 minutes.
Roda went ahead for the first time in the 74th minute when Nemeth got his second, but it ended all square with Jens Toornstra levelling in the 86th minute, just seconds before Utrecht's Yoshiaki Takagi saw red for a second caution.
Mark Uth hit a hat-trick as Heracles Almelo ran out 4-1 winners at RKC Waalwijk.
Uth was on target after 10 minutes and then twice after the break, while Bryan Linssen (39) also got his name on the scoresheet.
Aurelien Joachim hit RKC's consolation in the 25th minute.