Harrison was 4 of 9 beyond the arc and was 7 of 14 overall from the floor. UMKC (8-13, 3-1 WAC) made 12 of 33 3-point attempts.
Seattle led 25-24 at the end of a tightly-contested first half as Jarell Flora made 5 of 7 from the floor, including a pair of 3-pointers, for 12 points before intermission.
The Redhawks went up by eight three minutes into the second, but UMKC erased that with an 11-2 spurt which tied it at 40 with 12:44 left. The Kangaroos later went on a 17-2 run - including 3-pointers by four different players - to take a commanding lead.
Flora finished with 21 for Seattle (10-9, 3-2) and Isiah Umipig added 20 points, including 11 of 12 free throws.