Complex sentence: Mackenzie had a brief spell as professional at the Onwentsia Club in Lake Forest, Illinois, during which time he played in the U.S. Open in 1904 and 1905, finishing 3rd and tied for 16th.
Split into simpler sentences: Mackenzie had a brief spell as professional at the Onwentsia Club in Lake Forest, Illinois. During his time there he played in the U.S. Open in 1904 and 1905, finishing 3rd and tied for 16th.