Mason-Griffin scored 38 points and Davis added 24 for the Sooners (12-8, 3-3 Big 12), who are 10-0 at home and 2-8 on the road.
Iowa State (12-8, 1-4) had six double-figure scorers, led by Diante Garrett's 17.
Craig Brackins, who had been averaging 16.0 points and 7.8 rebounds, was held to 13 points and six rebounds.
Oklahoma led by 18 points, but Iowa State cut the deficit to three points four times in the second half, the final time with 6 seconds left. The Sooners clinched it by making 7 of 8 free throws in the final two minutes.
Maryland point guard Melo Trimble has withdrawn from the NBA draft and will return to College Park for his junior season, sources told ESPN.
Louisville's Chinanu Onuaku, who recently underwent a medical procedure to correct a heart rhythm issue detected during the combine, will keep his name in the NBA draft pool.
Andrew White III will return to the Nebraska men's basketball team next season after removing his name from the NBA draft.