The Cuban southpaw got off to a good start by catching Katsidis early on with sharp left hands, dropping him twice in the first round. As the fight continued, Katsidis' harder punches and constant pressure began to find their way through Casamayor's defence, at one point sending him tumbling through the ring ropes towards the end of round six, after successive left and right hands by Katsidis. In the ninth round, Casamayor was docked a point due to a low blow. All of this enabled Katsidis to gradually build up a lead on two of the judges' scorecards, until a well-placed counter left hand from Casamayor caught him on the chin in the tenth round, flooring him for a fourth time. Barely able to stand up, Katsidis was able to carry on but shortly afterwards a further flurry of unanswered shots from Casamayor forced referee Jon Schorle to stop the fight. This handed Katsidis his first defeat and cost him the WBO interim lightweight title. Again, cuts and bruises were noticeable around his eyes after the fight.