Benschop headed home a cross from Brett Holman after 33 minutes to open the scoring and sealed Alkmaar's first league win since December 10 with goals in the 47th and 69th minute.
A defence-splitting pass from Johan Gudmundsson set up Maarten Martens for another goal before Jozy Altidore added a double to complete the rout.
Alkmaar climbed to second on goal difference behind PSV Eindhoven with 42 points after 20 matches.
Steve McClaren's Twente Enschede are third with 39 points and a game in hand.
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