The Bluejays improved to 8-1, winning their second in a row since dropping a decision against Boise State.
McDermott made 10-of-19 shots from the field and grabbed five rebounds. Gregory Echenique had 12 points and 12 rebounds for Creighton.
The Bluejays had only a two-point lead with 6:30 to play in the opening half, but closed the period on a 14-5 run.
Nebraska (6-2), which had won two in a row, was led by 14 points from Dylan Talley and 10 from Brandon Ubel.