Katsidis was scheduled to face then-WBO super featherweight champion Joan Guzmán on 26 May 2007, but the latter withdrew from the fight due to a hand injury. Katsidis later defended his WBO interim lightweight title against Czar Amonsot on 21 July 2007 at the Mandalay Bay Events Center in Las Vegas, Nevada. This was Katsidis' first fight in the United States, as well as the first of his many appearances on the HBO network, as part of the pay-per-view undercard to Bernard Hopkins vs. Ronald "Winky" Wright.