It matched the second-highest playoff point total of Westbrook's career, falling short of the 43 he scored in the 2012 NBA Finals. He also had five rebounds and five steals.
Kevin Durant added 31 points on 11-for-22 shooting. It was his highest-scoring game of the series after he was held to a 22.7-point average in the first three games. Serge Ibaka added nine points and eight rebounds for the Thunder.
Boris Diaw had 14 points and 10 rebounds, and Tony Parker added 14 points for the Spurs.
San Antonio will host Game 5 on Thursday.