Isner on course for Atlanta Open hat-trick

Top seed Isner won a battle of attrition against the unseeded qualifier, converting his second match point to triumph 4-6 6-2 7-5 in one hour 43 minutes under a blazing afternoon sun on the outdoor hardcourt.

The match appeared to be heading to a tiebreak in the third set before Isner rallied from 30-0 down in the 12th game. He eventually clinched victory when Kudla uncharacteristically sent a crosscourt backhand sailing wide.

Isner said a more aggressive approach to his service returns in the second set was the key to victory.

"That 2-1 game in the second set turned the match around," the 30-year-old told ESPN. "My shots found the court, I was able to break and it relaxed me a lot from there.

"When I'm up a break I tend to serve my best because most of the time when I get one break I can take that set home."

Isner, who lost a five-set thriller to Marin Cilic in the third round at Wimbledon last month, has won nine ATP titles.

He next faces Gilles Muller of Luxembourg or Cypriot Marcos Baghdatis who meet in the other semi-final on Saturday evening.