[1] He began playing professional baseball in 1910 with the Vincennes Alices in the Kentucky–Illinois–Tennessee League.

In 1911, he continued in the minor leagues, playing for Vincennes as well as the Cairo Egyptians.

[2] In 1912, he reached the major leagues, playing for the St. Louis Browns.

[1] In mid-September 1912, the Browns sent Jantzen to the Montgomery Rebels of the Southern Association.

[2] Jantzen continued playing professional baseball until 1921, including stints with the Little Rock Travelers of the Southern Association (1915–1916), Chattanooga Lookouts (1916), and Bloomington Bloomers of the Illinois–Indiana–Iowa League (1919–1921).