The Houston Astros signed Watson as an amateur free agent in January 1965. He nearly quit baseball while playing in Minor League Baseball for an affiliate based in Savannah, Georgia, due to segregation in restaurants and hotels. Nicknamed "Bull", Watson converted to first base and the outfield by the time he made his major league debut with the Astros on September 9, 1966. Watson was a dependable hitter whose home run numbers were somewhat hurt by the fact that he played the majority of his career in the Astrodome, which had a reputation for being a pitcher-friendly ballpark.