Knowle was a successful player on the ATP Challenger Series, winning the Challenger tournaments in Kyoto (1999), Caracas (2001), Graz (2001), and Andrezieux (2002), and reaching the finals in Yokohama (2000), Bristol (2000), Besançon (2000), and Graz (2003). He also won several Futures tournaments.
Knowle was a successful player on the ATP Challenger Series, winning Challenger tournaments in Kyoto (1999), Caracas (2001), Graz (2001), Andrezieux (2002), and reaching the finals in Yokohama (2000), Bristol (2000), Besançon (2000), and Graz (2003). He also won several Futures tournaments.