Le'Bryan Nash scored 21 points and Phil Forte added 20 for the Cowboys (17-10, 5-9 Big 12), who forced 15 turnovers.
The Red Raiders had won three of five, with the two losses to Top 25 teams Iowa State and Kansas coming by a combined seven points.
Oklahoma State honored the late Bob Kurland at halftime. The 7-foot center was a three-time first-team All-American and led OSU to its only two national championships.
The teams were relatively even through most of the first half until Oklahoma State got into a rhythm. It started with a defensive play. Markel Brown tipped the ball to Smart, who passed the ball behind his head back to Brown, who finished with a layup. A steal and layup by Smart and 3-pointers by Forte and Brown helped Oklahoma State take a 24-14 lead and caused Texas Tech to call a timeout.
The Red Raiders closed the gap to 30-25 before Smart finished the half with a flurry. He drove to the hoop and made a layup in traffic with 8 seconds left in the half, then stole the ball and scored again a second later to help the Cowboys take a 34-25 lead at the break.
Turner, Tech's point guard, played just 4 minutes in the first half because of foul trouble. The Red Raiders' offense improved once Turner returned to the game, but the Cowboys responded to Tech's surge. Dunks by Nash and Kamari Murphy put Oklahoma State up 44-35.
Later, Smart got a steal, then the Cowboys pushed the ball downcourt and Smart found Brown for a layup. On Oklahoma State's next possession, Leyton Hammonds' 3-pointer bumped the Cowboys' lead to 59-42.
A left-handed jam by Smart gave Oklahoma State and 80-60 lead with just over 2 minutes to play.