John Isner. Pic/AFP

John Isner's magical ATP Miami Open run continued Wednesday when the big serving American overpowered South Korean Chung Hyeon 6-1 6-4 to book his place in the semi-finals. Isner, the 14th seed, arrived in South Florida having won just two matches all year, but his fourth victory of the week was enough to put him within touching distance of his first ATP Masters title. Isner will next face either Argentina's Juan Martin del Potro or Canada's Milos Raonic, who play in a later quarter-final.