ATLANTA -- Top seed John Isner won a hard-fought tiebreaker in the first set and held off teenager Jack Sock on Friday night to advance to the Atlanta Open semifinals.
Isner led 4-1 in the first set before losing his momentum after a rain delay of 1 hour, 4 minutes and recovering to beat Sock 7-6 (7), 6-4.
"I came out flat after the rain delay," Isner said. "Had it not rained, I think I could have won the first set a little more easily. That took a little out of me."
Isner will play Andy Roddick on Saturday night in a matchup of top Americans headed to the London Olympics after the tournament. Roddick, the No. 4 seed, beat Michael Russell 6-3, 6-4 on Friday night.
Sock, 19, challenged Isner with his persistent drop shots and devastating forehand winners. But Sock's mistakes, including two double-faults in the tiebreaker, were too much to overcome. Isner finally won the first set on his ninth set point.
The second set was tied 4-4 when Isner broke Sock's serve. The 6-foot-9 Isner then used his 130 mph serve to finish the win.
Humidity covered the stadium after the rain, making for what Isner called "gross" playing conditions.
"We were both sweating like pigs," Isner said. "Honestly, it was disgusting."
Sock, a wild-card entry from Lincoln, Neb., was making his first appearance in an ATP quarterfinal.
"He's got a big game," Isner said of Sock. "He hits the ball huge. He's only going to keep getting better. He's got a lot of good things ahead of him."
Isner, the former University of Georgia standout, is attempting to play in his third straight Atlanta final. He lost to Mardy Fish in the previous two finals. Fish withdrew Thursday with a right ankle injury.