psv beat heerenveen to lift their first eredivisie title in seven years .
ajax , who won the title for four successive years , are behind in second .
luuk de jong and memphis depay starred as psv eased to 4-1 win .
dordecht are on the verge of relegation after 3-0 loss to vitesse arnhem .
az alkmaar qualified for the europa league play-offs with 3-1 win .