Westbrook underwent his third knee surgery in nine months on Friday, an arthroscopic procedure that is expected to keep him out of action until after the All-Star break.
The defensive battle was close throughout with Oklahoma hitting 41 percent of its shots from the field and Charlotte managing only 38 percent.
Sefolosha and Serge Ibaka both had 12 points for Oklahoma City.
Kemba Walker scored 18 points for the Bobcats, but made just 6-of-17 shots from the field.
The Thunder won their second in a row and improved to 24-5, moving them into a tie with Portland for the lead in the Northwest Division.