McGruder finished 10 of 11 from the field, including 2 of 3 from 3-point range. He also went 6 of 7 from the line.
Will Spradling added 17 points for the Wildcats (10-1).
Larry Anderson and Casper Ware each scored 17 points for the 49ers (7-6).
The Wildcats went on a 29-13 run for a 38-22 lead with 2:27 left in the first half. McGruder had eight points, including two 3-pointers, during the surge.
In the first half, the Wildcats shot 17 of 33, forced 10 turnovers and outscored the 49ers 22-10 in the paint.
Spradling's 3-pointer gave Kansas State its biggest lead at 49-31 with 15:43 remaining. Long Beach State got as close as 62-52 with 6:41 to play.