Fleishman was born in Santa Monica, and attended UCLA for one year before turning pro.

At the age of 18, he played one season (1998–99) of collegiate tennis at the University of California at Los Angeles (UCLA), at the No.

In 2008, Zack added another professional tournament victory to his resume winning the Costa Mesa Tennis Futures.

In his career Fleishman notably defeated Fernando González, David Nalbandian, Vince Spadea, Agustín Calleri, Mardy Fish, Robby Ginepri, Daniel Nestor, Tomáš Berdych, Kei Nishikori, Kevin Anderson, Santiago Giraldo, Yen-Hsun Lu, Denis Istomin, Nicolas Mahut, and Joachim Johansson.

He proceeded to beat fellow American Robert Kendrick, in the second round, compiling his first ever back-to-back wins in an Association of Tennis Professionals event.

In September 2008, Fleishman won the USA F23 in California, beating Michael McClune in the finals in three sets.