Drew Crawford contributed 15 points and six assists for Northwestern (14-18), which will take on the third-seeded Michigan State Spartans in Friday's quarterfinal round. Dave Sobolewski added 10 points for the Wildcats.
For Iowa (20-12), Roy Devyn Marble netted a game-high 25 points on 8-of-18 shooting from the floor. Jarrod Uthoff provided 17 points and nine boards in 22 minutes off the bench, while Mike Gesell missed all 10 of his field goal attempts and finished with just one point.
Although Northwestern shot an even 50 percent from the floor in the opening period, the Hawkeyes held a narrow 31-28 lead with only seconds remaining before the break. Demps sank a 3-point attempt as time expired to send the contest into halftime tied. Iowa made good on 6-of-15 tries from behind the 3- point line in the opening 20 minutes of the contest.
The Wildcats took control in the second stanza as they shot 55 percent from the floor, including a 6-of-11 clip from beyond the arc. Iowa was limited to 25.7 percent efficiency from the field and missed all nine of its shots from 3-point range after halftime. Northwestern led for the final 7:56 of the game.
Iowa defeated the Wildcats by a 26-point margin in both regular season meetings this season. Northwestern is the only school from a major conference that has still never made a trip to the NCAA Tournament.