Top-seeded Jack Sock led three Americans into the US Men's Clay Court Championship semi-finals, beating sixth-seeded Feliciano Lopez of Spain 7-6 (6) 1-6 6-4.
Sock won at Forest Oaks in 2015 for his first ATP Tour title and added victories this year in Auckland, New Zealand, and Delray Beach, Florida.
Sock will face fourth-seeded countryman Steve Johnson, a 6-2 6-4 winner over fifth-seeded Fernando Verdasco of Spain.
Johnson won his lone tour title last year on grass at Nottingham in England.
Ernesto Escobedo reached his first ATP Tour semi, outlasting second-seeded John Isner 7-6 (6) 6-7 (6) 7-6 (5) in an all-American match.
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The 20-year-old Escobedo overcame a 35-10 ace disadvantage against the 2013 tournament winner.
Escobedo will face eighth-seeded Thomaz Bellucci of Brazil, a 6-4 3-6, 6-3 winner over third-seeded American Sam Querrey.
