Russell Westbrook led the Thunder (36-12) with 24 points on 8-of-16 shooting, including going 8-of-9 from the free throw line and adding seven assists and three steals. Kevin Durant added 19 points and 10 rebounds on the night.
Shawn Marion led the way for Dallas with 23 points.
The first half sealed the Mavs' fate as they were outscored 68-44 through the first two quarters. They shot just 45.5 percent from the field and went 0-for-6 from the three-point line in the half. Dallas (20-28) committed 14 turnovers on the night and gave up 17 points off giveaways, including 21 fast-break points to the Thunder.
Oklahoma City led by as many as 33 points and used a 48-40 rebounding advantage to overcome Dallas' runs. Though the game featured five lead changes and seven ties, it was never close after the half.