Westbrook outdueled James Harden, who finished with 29 points but had a 3-point attempt fall short in the final minute. Westbrook grabbed the rebound, pushed it up to Andre Roberson cutting to the basket and Roberson finished it off to put the game away.
Both teams' biggest scoring weapons struggled from the floor early before coming on strong in the third.
After scoring 50-plus points in each of his last two games, Rockets guard James Harden was just 1 of 7 from the floor in the first half, relying instead on getting to the free-throw line and creating for his teammates early.
But Harden ignited in the third quarter, going 4 of 6 from the floor, scoring 14 with five assists as Houston took the lead heading into the final 12 minutes.
Russell Westbrook was just 4 of 14 from the floor at halftime but was more aggressive in the third, making all five of his third-quarter field-goal tries.
Westbrook hit his first two shots of the fourth as well before finally missing with less than five minutes remaining.
He finished 8 of 10 from the floor in the first half.
The Rockets were playing without Chris Paul, who missed his second consecutive game with a left adductor strain.
Before the game, Houston coach Mike D'Antoni said Paul was still a few days away from being able to return.
Houston doesn't play again until Thursday in Boston, the start of a back-to-back. D'Antoni said he was hopeful Paul could play in one of those two games but wouldn't play in both.
NOTES: Thunder G Andre Roberson left the game early with a dislocated finger on his left hand. He returned from the locker room a few minutes later with the middle and ring fingers on the hand taped together. ... Houston C Clint Capela returned to the lineup after missing the last two games with a left heel contusion. ... Thunder C Steven Adams scored 15 points -- 12 in the first quarter and all by halftime. ... The Rockets are 5-5 all-time on Christmas Day, while Oklahoma City is 6-13. The franchise was 0-11 on the holiday before moving from Seattle. ... The Thunder have played on Christmas Day eight consecutive seasons, the second-longest streak in the league. The Los Angeles Lakers have played on every Christmas since 1999.