The victory was the 158th at Oklahoma (9-2, 6-2 Big 12) for Coach Bob Stoops, who passed Barry Switzer to become the winningest coach in school history.
Clay scored on a 3-yard carry early in the fourth quarter that staked the Sooners to a 34-24 lead. Zack Sanchez followed up with a 74-yard interception return for a TD.
Trevor Knight started at quarterback for Oklahoma in place of injured Blake Bell. He threw for 171 yards and a touchdown, and also ran for 82 yards and a score.
Tyler Lockett caught three touchdown passes and had 162 yards on kickoff returns for Kansas State (6-5, 4-4). Jake Waters completed 17-of-29 passes for 348 yards and three touchdowns.