Oklahoma City held Memphis to 12 second-period points, built a 24-point halftime lead and coasted the rest of the way while hitting 55 percent of its field goal attempts.
Durant scored 27 points and Westbrook had nine rebounds and six assists to go with his 21 points. Kevin Martin added 16.
The Thunder won their 20th home game in 23 tries.
Jerryd Bayless produced 23 points to lead the Grizzlies, who have lost six of their last 11.