On Wednesday, John Isner's magical ATP Miami Open run continued 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.

The 32-year-old American fired 13 aces to dispatch 19th-seeded Chung in only 68 minutes. "The conditions were perfect for me. The way the ball bounces, the court isn't too fast, so it's great for me. I have played well here before but I am delighted to get this far."

Chung, playing in his sixth last-eight match of the year, defeated Isner in their previous meeting in Auckland but was unable to stay in the match after being steamrolled in an opening set that saw him broken for the first time this tournament.

"His serve made it very difficult and I gave him some easy points," Chung said. "My returns weren't good enough but I'm satisfied with my progress this year. "I've felt good ever since reaching the semi-finals of the Australian Open. But losing matches always hurts." Isner stressed he`s not been doing anything different at this tournament even though he arrived in Miami in such poor form.