structural:reformatting, structural:expansion, quality:correction
Professional career

In 1959, he signed his first professional contract as a pitcher for the Yomiuri Giants. However, Oh was not a strong enough pitcher to succeed professionally, and soon switched to first base, working diligently with coach Hiroshi Arakawa to improve his hitting skills. This led to the development of Oh's distinctive "flamingo" leg kick. His batting average jumped from.161 in his rookie season to.270 in 1960, and his home runs more than doubled. His performance dipped slightly in both statistical categories in 1961, but Oh truly blossomed in 1962, when he hit 38 home runs.

In 1964, Oh hit 55 home runs, a single-season record he owned for 37 years until it was tied by Tuffy Rhodes in 2001. Oh surpassed 50 home runs in a season two other times, in 1973 and 1977.

Oh became friends with Hank Aaron, his contemporary in Major League Baseball. The two squared off in a home run derby before an exhibition game at Korakuen Stadium on 2 November 1974, after Aaron eclipsed Babe Ruth 's home run record. By that time, Oh was running away with the Japanese home run record, having become the first Japanese baseball player to hit 600 career home runs that year. Aaron won, 10–9.

His hitting exploits benefited from the fact that for most of his career he batted third in the Giants' lineup, with another very dangerous hitter, Shigeo Nagashima, batting fourth; the two players forming the feared "O-N Cannon". In his autobiography, Sadaharu Oh: A Zen Way of Baseball (ISBN 978-0812911091), Oh said he and Nagashima were not close, rarely spending time together off the field.

Sadaharu Oh retired in 1980 at age 40, having amassed 2,786 hits (third after Isao Harimoto (Jang Hoon) and Katsuya Nomura), 2,170 RBIs, a lifetime batting average of.301, and 868 home runs.