The Polish international had been restored to the team three weeks ago and has since responded with key goals to keep Ajax breathing down the neck of PSV in what is now a two-team race for the title.
Milik broke the deadlock just before the break and team mates Riechedly Bazoer, Lasse Schoene and Davy Klaassen added three more goals after half-time.
Ajax have now won five league games in a row and advanced to 64 points. PSV are on 65 after winning on Saturday at Groningen.
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“We are keeping it nice and exciting. It’s an absorbing title race for everyone to follow but hopefully we can pull away near the end,” Klaassen told Dutch television after the victory.
Feyenoord returned to third spot as they beat SC Cambuur 3-1 and are just ahead of AZ Alkmaar on goal difference. The pair are 22 points off the top of the table.
Jens Toornstra scored Feyenoord’s opening goal in the first half, but the visitors drew level 20 minutes from the end as Martijn Barto equalised.
Further goals from Dirk Kuyt and Eljero Elia turned the game in the home side’s favour though.
AZ Alkmaar’s 2-0 home win over struggling Excelsior came through second half goals from Derrick Luckassen and Vincent Janssen, who converted a penalty.
Chinese substitute Zhang Yuning scored a stoppage time winner as Vitesse Arnhem kept themselves in the chase for a Europa League spot next season as they won 2-1 at Roda JC Kerkrade.
Christian Santos scored the winner two minutes from the end as NEC Nijmegen beat Heracles Almelo 1-0 to also stay on course for a place in European competition.
(Reporting by Mark Gleeson in Cape Town, editing by Pritha Sarkar)
