There were six ties and eight lead changes in the first half before Ballock hit a 35-foot buzzer beating 3-poiner to put the Bluejays on top 43-41 at the break.
Creighton ended up at 46 percent, making 11 of 23 3-pointers.
Kobe Webster had 24 points and 10 rebounds for Western Illinois, which shot 36 percent, making just 9 of 29 from distance. Isaac Johnson added 19 points and nine rebounds. The Leathernecks were 8 of 9 from the foul line, where the Bluejays were 9 of 20.