Guard Trey Demps hit a 3-pointer with 55 seconds left, breaking a 52-52 tie and lifting the Wildcats to a 55-54 victory.
Guard JerShon Cobb scored 15 points and forward Drew Crawford had 17 the Wildcats, who made a little history.
By forcing the Gophers to slow the pace, getting key defensive stops late and making clutch shots down the stretch, the Wildcats (12-11, 5-5 in the Big Ten) won their third straight road conference game for the first time since 1959-60 season.
That was 14 years before first-year Northwestern coach Chris Collins was born.
The Gophers (15-7, 4-5), got 13 points from guard Austin Hollins and 14 from center Mo Walker. Still, they dropped their second straight game and third in four games.
With the score tied, 47-47, Crawford hit a 3-pointer with 6:12 left.
The teams traded misses until Crawford was fouled and hit both free throws with 1:53 left. Gophers guard Malik Smith answered in the lane 21 seconds later.
Enter Demps, who dribbled the ball as the shot clock ticked down, then hit the 3-pointer with 55 seconds left for the final three of his 11 points.
Mathieu scored in the lane nine seconds later.
With 11.9 seconds left Demps missed, setting up the Gophers, down one, for a final possession. Mathieu missed on a drive, then Walker missed on a put-back as time expired.
Northwestern opened the game hitting 5-of-8 3-pointers, led by Cobb, who was 3-for-3, while building a 21-11 lead.
Then it was the Gophers' turn.
Walker had six points in a 10-0 run that pulled the Gophers into a 21-21 tie on his post move with 6:26 left.
But Northwestern finished the half on a 9-2 run, started by consecutive hoops by Crawford and a 3-pointer by Kale Abrahamson with seconds remaining in the half to give the Wildcats a 32-29 lead.
NOTES: This was the first time the two first-year coaches in the Big Ten met. ... It was a homecoming for Northwestern F Sanjay Lumpkin. The redshirt freshman is from the Minneapolis suburb of Wayzata. He is the son of former University of Minnesota football player Sean Lumpkin and is the stepson of former Minnesota and NBA basketball player Jim Petersen. ... Minnesota guard Andre Hollins missed his second start because of a sprained ankle sustained in the first few seconds of the Gophers' victory over Wisconsin on Jan. 22. Hollins is expected to miss one more start before returning Feb. 8 vs. Indiana.