Ejim finished with 22 points and 16 rebounds for the Cyclones (16-4, 4-4 Big 12), who claimed a second victory in three games.
Matt Thomas chipped in 13 points and Monte Morris added 12.
The Sooners (17-5, 6-3) had their four-game winning streak snapped despite 30 points from Buddy Hield.
Isaiah Cousins totaled 13 points and 10 rebounds.
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