Marshall was 5 of 9 from the field, including 4 of 7 from long range. Deondre Parks and Cody Larson chipped in 14 points apiece for South Dakota State (10-7, 1-2 Summit League), which snapped a four-game losing streak.
The Jackrabbits led 34-20 at the break, and opened the second on a 12-7 surge to stretch their lead to 46-27 with 14:43 to play. Jake Bittle scored five points during an 11-0 run to make it 63-31 with about six minutes left.
Garret Covington and J.C. Fuller each scored 11 points for Western Illinois (7-7, 2-1), which shot just 18 of 58 for 31 percent from the floor. The Leathernecks were held to under 51 points for the fourth time this season.