PSV went into their match undefeated in the Dutch top-flight this season, but fell behind courtesy of Nick Viergever's 21st-minute opener for the hosts.
And, though Memphis Depay levelled for the visitors just before the break, Aron Johannsson secured all three points for AZ in the 57th minute.
That slip-up allowed Ajax to close the gap at the top of the table to just one point, after they romped to a 6-0 triumph against Go Ahead Eagles at the Amsterdam Arena.
It was the perfect response from the Amsterdam outfit, who suffered a heavy 4-0 defeat to rivals PSV last Sunday.
Incredibly, all of the goals came in the second half, as four strikes in just five minutes put Frank de Boer's men in complete control.
Jop van der Linden put past his own goalkeeper in the 48th minute before Lesley de Sa and a Kolbeinn Sigthorsson double gave Ajax a four-goal cushion.
And the rout continued as two strikes in five minutes from Lerin Duarte and Siem de Jong completed an excellent spell for the defending champions.
Elsewhere, RKC Waalwijk slumped to a fourth straight league defeat as they were humbled 4-1 at home by Heracles at the Mandemakers Stadion.
Mark Uth and Bryan Linssen strikes sandwiched Aurelien Joachim's equaliser as the visitors led 2-1 at half-time.
The second half was dominated by Heracles, with Uth adding two more to complete an impressive hat-trick.
At the Stadion Galgenwaard, Utrecht and Roda JC played out an entertaining 3-3 draw.
Cedric van der Gun saw his opener cancelled out by Krisztian Nemeth, but Utrecht still led at the break thanks to an own goal from goalkeeper Filip Kurto.
The visitors came out strong in the second half, however, as Mark-Jan Fledderus' goal and a second from Nemeth put them ahead for the first time in the game.
But they could not hold on to the three points, with Jens Toornstra grabbing the equaliser in the 86th minute.
In Saturday's other fixture PEC Zwolle were held to a 0-0 draw at home by NAC Breda.
