Lewis finished with 21 points for the Vikings (4-4), who scored 13-straight midway through the first, led 44-21 at halftime and extended to their largest lead at 74-45 with 4:15 left.
Anton Grady had 14 points and Andre Yates added 11 with a perfect 4-of-4 from the field, including three 3-pointers. Yates also had four steals to key a defensive effort that caused 15 Western Illinois turnovers in the first half and 21 overall.
Garret Covington had 17 points and Jabari Sandifer scored 12 for WIU (2-5). The Leathernecks (46.7 percent) had comparable shooting with Cleveland State (48.1), but their struggles to possess the ball led to seven less field goal attempts and 13 less free-throw attempts.