America's Ryan Sweeting escaped six break points in the final game to upset second-seeded countryman Sam Querrey 3-6, 7-6 (5) 6-3 in the second round of the U.S. Men's Clay Court Championships on Wednesday.
There were 11 total service breaks in the match. The players broke each other in seven consecutive games, spanning from the last five games of second set through the first two games of the third.
Sweeting survived 18 of 24 break points. Querrey lost three points on his serve in the tie-breaker, including a double-fault for set point.
"I just don't feel comfortable on clay yet," Querrey said. "I need to just put a couple of weeks of practice in there and get ready for the next tournament."
Fourth-seeded John Isner of the United States downed Argentina's Horacio Zeballos 7-5, 6-3, while Teymuraz Gabashvili of Russia defeated eighth seeded Grigor Dimitrov of Bulgaria 7-6 (4), 6-3.
Qualifier Ivo Karlovic of Croatia boomed over 12 aces to beat Igor Kunitsyn of Russia 6-4, 6-1.
Isner served up 14 aces and did not face a break point in his match.
"I actually enjoy playing on clay but the first one is very tough," Isner said. "The movement is very different and I only got to practice four or five times on clay. I was just trying to get through."
Isner, who is 6-foot-9 (2.06 meters), will play 6-10 (2.08-meter) Karlovic next.
"It's not often I get to look eye to eye with someone and he's the same," Isner said.