Murakami entered the Japanese Pacific League professional team, the Nankai Hawks, in September , while still attending high school. In 1964, his team sent him, along with two other young players, to the San Francisco Giants single-A team Fresno as a baseball "exchange student". He was originally only scheduled to stay in the United States until June, but the Hawks neglected to call him back to Japan, and he stayed with the Giants for the rest of the season. In August of the same year, he was promoted to the majors, and on September 1, 1964, he became the first Japanese player to play in the major leagues and the first Asian-born player since Chinese-born Harry Kingman's cup of coffee 50 years earlier. He entered the ninth inning against the New York Mets and pitched to four batters, striking out two and allowing just one hit and zero runs. He pitched the final three innings of an 11-inning 5-4 win by the Giants on September 29 over the Houston Colt .45s to get his first career win. In nine games with the Giants, he pitched a total of 15 innings while allowing eight hits and three runs (with all of the runs occurring in his final game on October 4th) while having 15 strikeouts and one walk for a 1.80 ERA. Murakami's performance caused the Giants to refuse the Hawks' order to return him to Japan. The argument escalated during the 1964 off-season, and Japanese baseball commissioner Yushi Uchimura was called in to make the final decision on which team Murakami would play with. The commissioner made a compromise; Murakami would return to the Hawks after he had played for another full season with the Giants. He wore number 10 with the San Francisco Giants. He appeared in 45 games, pitching a total of 74 1⁄3 innings while going 4-1 with a 3.75 ERA, 85 strikeouts and 22 walks.