LONDON, ENGLAND - JUNE 30: John Isner of the United States prepares to serve during his Gentlemen's Singles third round match against Feliciano Lopez of Spain on day seven of the Wimbledon Lawn Tennis Championships at the All England Lawn Tennis and Croquet Club on June 30, 2014 in London, England. (Photo by Jan Kruger/Getty Images)

Atlanta – Defending champion John Isner and Jack Sock each rallied from early deficits to set up an all-American semifinal in the Atlanta Open.

Isner was not sharp in beating Marinko Matosevic 7-6 (8), 6-4 in hot conditions, but took advantage of the Australian's mistakes. Sock later topped Slovakia's Lukas Lacko 7-6 (6), 6-2.

In the other quarterfinals, Germany's Benjamin Becker beat Dutchman Thiemo de Bakker 6-4, 6-2, and Israel's Dudi Sela upset fourth-seeded Vasek Pospisil of Canada 7-5, 1-6, 6-2.

Isner, the top seed, dropped his serve in the first game of the match and had to fight off break points in his second and third service games to make the semifinals for a fifth straight year.

He finished the match with his 17th ace, yet won a modest 70

percent of points on his serve, well below the ATP Tour-leading 93

percent rate he carried into the quarterfinals.

“I knew he was struggling out there a little bit, and he knew I was struggling a little bit,” Isner said. “A lot of times in situations like that ... even though I appear to be super tired and I am super tired, I can muster up enough energy to pop some big serves in.

“The beginning of that second set it felt like someone put us both in an oven.”

Isner won the event last year after falling in the 2010 and '11

finals to Mardy Fish and losing in the 2012 semifinals to eventual champion Andy Roddick.

Lacko led 5-3 in the first set against Sock, but the American rallied to force a tiebreaker and finish off his career-high 18th win of the season.

Sock, who won the Wimbledon doubles crown three weeks ago with Pospisil, beat Isner in straight sets this month on grass at Newport, and lost to him in May on clay in Nice. – Sapa-AP