Top-seeded John Isner of the United States beat South Korea's Chung Hyeon, 7-6 (5), 6-4, on Friday night in the U.S. Men's Clay Court Championship quarterfinals in Houston.
Isner will face the fourth-seeded defending champion Jack Sock of the United States, a 6-4, 6-4 winner over seventh-seeded Marcos Baghdatis of Cyprus.
In afternoon matches at River Oaks, Argentina's Juan Monaco beat fifth-seeded Sam Querrey, 6-4, 6-4, and third-seeded Feliciano Lopez of Spain topped American Tim Smyczek, 6-2, 6-3. The 32-year-old Monaco won the event in 2012.
In doubles, American twins Bob and Mike Bryan advanced to the final, beating Querrey and Steve Johnson 7-6 (5), 6-3. The Bryans have won the event five times and have 109 team titles.
Kerber advances in Charleston
Australian Open champion Angelique Kerber moved a step closer to her second straight Volvo Car Open title, reaching the semifinals in Charleston, S.C., with a 6-2, 6-3 victory over Irina Camelia Begu.
Kerber, the top seed, will face No. 7 Sloane Stephens, who defeated 14th-seeded Kasatkina, 6-1, 5-7, 7-5.
Errani defeated Yulia Putintseva of Kazakhstan, 7-6 (2), 6-1, while Vesnina topped Laura Siegemund of Germany, 7-5, 6-4.