On 2 March, a fight between Katsidis and then-undefeated lightweight challenger Kevin Mitchell was officially confirmed by promoter Frank Warren. It was contested on 15 May at Boleyn Ground stadium in London, with the WBO interim lightweight title on the line. At the opening bell, Mitchell looked to establish his jab and keep Katsidis at bay. In the first two evenly split rounds, the occasional flurry of hooks from a highly aggressive Katsidis was enough to make Mitchell fight consistently on the back foot in an attempt to keep out of range. However, in the closing seconds of both rounds, Katsidis was able to launch a charging attack and finish strongly at the bell. In the third round, Katsidis continued to charge at Mitchell and was soon able to land a combination of hooks which made the latter stumble backwards on unsteady legs. From thereon, Mitchell was unable to fully regain his composure and, less than two minutes later, he was buckled by a hard left hook and a further succession of unanswered punches, at which point referee Dave Parris stopped the fight.