Katsidis' next fight took place on 9 April 2011 against Robert Guerrero, in a rescheduling of their cancelled fight from March 2010. Staged at the MGM Grand, it formed part of the pay-per-view undercard to Érik Morales vs. Marcos Maidana. The WBA and, once again, WBO interim titles were at stake. Despite an animated taunt of "What are you looking at?!" from Katsidis to Guerrero during their pre-fight staredown, a fourth career defeat would await Katsidis in his most one-sided to date. Guerrero was able to maintain a safe distance by consistently landing accurate punches with his jab and straight left hand, to which Katsidis had virtually no answer at any stage in the fight.