John Isner is just two wins away from a fourth Atlanta Open title in five years after outbattling Lukas Lacko in Friday's quarter-final.

The second seed has an impeccable record at the Atlantic Station and saw a three-year winning streak ended only in the final by Nick Kyrgios 12 months ago.

And Isner took a step closer to regaining the trophy with a 7-5 6-4 victory, with a solitary break in each set enough for the win.

Standing in his way of playing a fifth straight final is third seed and 2012 runner-up Gilles Muller, who comfortably dispatched of Tommy Paul 6-3 6-1.

On the other side of the draw, top seed Jack Sock was beaten by fifth Kyle Edmund 6-4 6-1.

Fourth seed Ryan Harrison will be his semi-final opponent following the American's 6-1 6-2 hammering of compatriot Christopher Eubanks.