Dee ihe ga-aga n'ihu maka paragraf a - Jansen laghachiri na Pacific Coast League dị ka onye ọkpụkpọ-onye nchịkwa na Seattle (1955 na 1957) na Portland (1958<unk>60). Mgbe onye otu ya bụ Alvin Dark kpọrọ ya oku, Jansen laghachiri na Major Leagues dị ka onye nkuzi pitching maka San Francisco Giants na, na Dark dị ka onye njikwa. Jansen nọgidere dị ka onye na-enye ọzụzụ maka oge iri na otu, ma nyere aka ịzụlite Hall of Famer Juan Marichal na Gaylord Perry. N'oge ọ nọ n'ọchịchị, ndị Giants pụtara na 1962 World Series na 1971 National League Championship Series
Ọ dị mma. Mgbe ahụ, ọ gara n'ihu na ọrụ nchịkwa MLB ikpeazụ ya, na-ejikwa pitchers maka Chicago Cubs na <unk>73, na-arụ ọrụ maka onye njikwa Giants ochie ya, Leo Durocher, na mgbe ahụ onye otu ibe ya Whitey Lockman.