The two-time All-American McDermott contributed 27 points and didn't miss one of his 10 free throws in the opening round of the Wooden Legacy on Thanksgiving.
Devin Brooks scored 23 points for Creighton (5-0), which advanced to meet San Diego State in Friday's semifinals.
Jahii Carson had 15 points for the Sun Devils (6-1) but committed five turnovers; Jermaine Marshall and Richie Edwards each added 12 points in the loss.
Creighton shot 53.4 percent from the floor and 12-of-25 from behind the arc. Arizona State was 37.9 percent from the field and 7-of-26 from 3-point range.
The other semifinal sees Marquette taking on George Washington.