Ager, who entered Wednesday night averaging 15.6 points on 69 percent shooting against the Wildcats in five games, hit a 3-pointer with 3:33 left in the second half to squelch a Northwestern rally that had seen the Wildcats cut an 18-point deficit to five. He finished with 20 points, going 7-of-9 from the field (4-of-5 from downtown), to help Michigan State (21-5, 12-3 Big Ten) to a 69-58 victory over Northwestern.
Senior Alan Anderson continued his stellar play over the last month, leading Michigan State with 22 points. Anderson hit six-straight free throws over the final 1:24 to seal the win.
Paul Davis chipped in with 8 points and a game-high 12 rebounds for the Spartans.
Vedran Vukusic led Northwestern with 17 points and went over 1,000 for his career.
Rebounding from an overtime loss at Indiana, Michigan State won for the seventh time in eight games and beat Northwestern for the 33rd time in the last 35 meetings.
Meanwhile, Northwestern (14-14, 6-9 Big Ten) must win its finale at Indiana on Saturday to secure a winning season and keep hopes for an NIT bid alive.
Northwestern coach Bill Carmody got his second technical foul with 35 seconds left in the opening half and was ejected, missing his team's rally that fell short.
Carmody picked up his first technical with 7:56 left and Shannon Brown's free throw capped a seven-point spurt that gave the Spartans a 29-12 lead.
Kelvin Torbert made one of two free throws after Carmody's second technical, which was assessed for comments the coach apparently made during a timeout. The Spartans maintained possession and Torbert got inside for a layup with 5 seconds remaining in the half to put State ahead 37-22.
Northwestern missed 10 of its 21 free throw attempts and was only 3-for-16 from 3-point range. The Spartans had a 37-25 advantage on the boards, but were plagued by poor shooting of their own; hitting on only 6-of-20 (.300) from beyond the arc.
The Wildcats scrapped on defense in the second half, cutting Michigan State's lead to 57-51 on T.J. Parker's 3-pointer with 6:12 left that capped a 12-1 run.
Then, with a chance to cut the lead to four, a Northwestern turnover led to an Anderson score, followed soon by a Paul Davis' free throw that made it 60-51 with 4:50 left.
Northwestern would respond again when Vukusic hit a basket and then got two more points on a goaltending call by Torbert, making it 60-55 with 4:00 to play.
Ager's aforementioned triple soon followed, stretching the Spartan lead back to eight, 63-55. From there, Anderson's free throws sealed the win.
The Spartans final game of the regular season comes this Saturday night in East Lansing versus Penn State. Seniors Anderson, Torbert, Chris Hill, Tim Bograkos and Andy Harvey will be honored in their final appearance in the Breslin Center.