Senior forward Adreian Payne led the way for Michigan State with 20 points and 14 rebounds – his fifth double-double this season.
He is averaging more than 18 points per game in his past three since returning from a foot injury.
Denzel Valentine had a career-high 16 points, while Gary Harris had 14 and Travis Trice scored 11. Trice played his third straight game of turnover-free basketball -- spanning 102 minutes -- since Keith Appling went out with a right wrist injury.
Harris, who struggled shooting 3 of 20 in a loss to Wisconsin on Sunday, hit his first three field-goal attempts.
Matt Costello was the lone starter not in double digits, as he finished with nine points.
Junior guard JerShob Cobb led Northwestern with 22 points on 5 of 11 shooting from 3-point range.