Mike Rostampour and CJ Carter added 10 points each for the Mavericks (15-9, 4-4 Summit League), who won their third consecutive game.
Garret Covington scored 21 points and Jabari Sandifer 14 for the Leathernecks (9-14, 3-5), who dropped their second straight.
Western Illinois made 7 of 16 3-point attempts and 19 of 21 free throws, plus tied the Mavericks on the boards. But they only made 32.7 percent of their shots overall and were hurt by 19 turnovers as Omaha made 13 steals.
The Leathernecks tied the game with 8:42 left before Karhoff scored to give Omaha lead back at 8:27 at 47-45. The Mavericks extended the lead to 55-47 with 4:37 left and the Leathernecks wouldn't get closer than seven after that.
Omaha shot 42.6 percent.
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