Jack Sock beats John Isner in U.S. Clay semifinal

Fourth-seeded defending champion Jack Sock defeated top-seeded John Isner, 7-6 (4), 6-3, in an all-American semifinal in the U.S. Men’s Clay Court Championship at Houston.

“I love playing in this city, on this court. I love the clay,” said Sock, who has won 16 consecutive sets in this event. “There’s something about that little stadium there, it’s a great atmosphere.”

Sock will face Argentina’s Juan Monaco in the final Sunday. The 32-year-old Monaco, the 2012 winner, beat third-seeded Feliciano Lopez of Spain 6-4, 6-2.

“I’m really happy to be here again in the final,” said Monaco, an eight-time winner on the ATP Tour. “I was really focused, consistent from the baseline.”

The 6-foot-10 Isner had treatment on his left knee twice during the match.

“My body is a little beat up,” Isner said. “I haven’t been healthy in a while. We’ll see what I need to do. Got to pay the piper eventually.”

American twins Bob and Mike Bryan won the doubles titles for the sixth time, beating Victor Estrella Burgos of the Dominican Republic and Santiago Gonzalez of Mexico, 4-6, 6-3, 10-8 (match tiebreaker). The Bryans have 110 team titles.

“It was a battle from the first point to the last, but we feel like we played our best tennis down the stretch,” Bob Bryan said. “It’s nice to pull out some close wins after losing a few tight matches to start the season. We’re looking forward to building momentum through the clay-court season.”

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Australian Open champion Angelique Kerber, ranked No. 2 in the world, retired because of a viral illness during her semifinal match at the Volvo Car Open, sending American Sloane Stephens to the final in Charlotte, N.C.

Stephens will face Elena Vesnina, the Russian qualifier who upset fifth-seeded Sara Errani of Italy, 6-4, 4-6, 6-2, in the other semifinal. Vesnina, who reached the final in Charleston five years ago before losing to Caroline Wozniacki, is first qualifier to make the finals in the 44-year history of the tournament that started on Hilton Head Island.