The present invention is directed to a method of making a rubber composition, comprising the steps of A) obtaining a diene-based elastomer selected from the group consisting of natural rubber, synthetic polyisoprene, polybutadiene, solution polymerized styrene-butadiene rubber (SSBR), and emulsion polymerized styrene-butadiene rubber (ESBR); B) mixing the diene-based elastomer with a halogenating agent to form an intermediate elastomer; and C) mixing the intermediate elastomer with a carbon black. There is further disclosed a rubber composition made by the foregoing method, and a pneumatic tire comprising the rubber composition.