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Collarini had represented Argentina in the early days of his career from 2007 to 2010, until he chose to represent USA from 2010 to 2012 before switching back to represent Argentina.
On the junior circuit, Collarini had a career high ITF junior ranking of 5 achieved in 2009. In 2010, he reached the final of the French Open boys’ singles event, finishing runner up to Agustin Velotti.

Kolář has a career high ATP singles ranking of World No. 136 achieved on 1 November 2021. He also has a career high doubles ranking of World No. 114 achieved on 16 August 2021. Kolář played his first match in an ATP tournament, after qualifying in the 2018 Swedish Open. He was defeated in straight sets by defending champion and former Top 10 member David Ferrer.
