PSV won 3-1 at PEC Zwolle to move to 84 points from 34 games, two more than Ajax who were held to a 1-1 draw when victory would have made them champions on goal difference.
Luuk de Jong netted twice for PSV to take his season tally to 26 goals, one behind AZ Alkmaar's Vincent Janssen at the top of the scorers list, after Jurgen Locadia had given them an early lead.
It was a comfortable victory for manager Phillip Cocu to ensure back-to-back league titles at the expense of Ajax who will remember this day for many years as one of missed opportunity.
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They led the league for most of the season, only to falter against a team they have beaten in their last 13 meetings dating back to 2000.
Amin Younes gave Ajax a 16th-minute lead to set them on their way but Bryan Smeets equalised for De Graafschap 10 minutes after halftime when he drilled the ball into the corner of the net from the edge of the area.
Ajax had almost 60 percent possession and 21 shots on goal, but a precious second eluded them.
De Graafschap now enter the relegation playoffs along with Willem II, who could not escape the bottom three despite a victory at Roda JC.
Excelsior Rotterdam claimed a 2-0 win at relegated Cambuur to secure their survival while third-placed Feyenoord sealed a 1-0 home victory over NEC.
They will play in the Europa League next season along with AZ Alkmaar who finished fourth.
Utrecht, Heracles Almelo, Groningen and PEC Zwolle will contest the Europa League playoff competition.
(Reporting by Nick Said, editing by Ed Osmond)
