The Sooners will play Texas, the tournament's top seed, at 1 p.m. Saturday for the right to advance to the title game.
An offensive show it wasn't between the 12th-seeded Buffaloes and fourth-seeded Sooners.
Oklahoma held Colorado to just 34.6 percent (18-of-52) from the field, including 24 percent (6-of-25) from 3-point range.
The Sooners weren't any better from the field, making just 32.8 percent (19-of-58) overall and 26.1 percent (6-of-23) from 3-point range.
Oklahoma also didn't help itself from the foul line, making just 10-of-19 attempts, including 7-of-14 in the second half. The Sooners, at one point, missed four straight free throws while trying to extend a slim lead over the Buffaloes in the final minute.
However, the Sooners did out-rebound Colorado 46-37 and never trailed in the game.
In fact, Oklahoma jumped out to a 10-0 lead and held Colorado scoreless for the first 5:05. Oklahoma led 26-21 at the half and has now held its opponents to 30 or fewer points in seven of the last eight halves its played.
Tony Crocker led Oklahoma's scoring charge with 12 points, including a pair of 3-pointers.
Blake Griffin played just 15 minutes. He scored just four points, tied for his lowest output of the season, but did add nine rebounds.
Colorado was led by Richard Roby's 18 points and 10 boards.
Oklahoma won its fourth straight game and improved to 22-10.
The Sooners are now 19-8 overall in the conference tournament's 12 years (winning it three times) and have won at least one game 10 times.