Sock survives, Isner outlasted in Houston

Jack Sock and John Isner had contrasting days at the US Men's Clay Court Championship in Houston.

Top seed Jack Sock battled into the US Men's Clay Court Championship semi-finals, but John Isner was outlasted in a marathon clash.

Sock, finalist in Houston the past two years and winner in 2015, got past Feliciano Lopez 7-6 (8-6), 1-6, 6-4 in two hours, 14 minutes on Friday.

The American broke twice in the third set at the ATP 250 event, reaching a fourth semi-final of the year.

Sock holds a 20-4 win-loss record this year, including titles in Auckland and Delray Beach.

Awaiting Sock in the last four is Steve Johnson, the American fourth seed having cruised past Fernando Verdasco 6-2, 6-4.

Isner, the second seed and 2013 champion, was edged by fellow American and wildcard Ernesto Escobedo 7-6 (8-6), 6-7 (6-8), 7-6 (7-5).

It took just over three hours for 20-year-old Escobedo to get through, with only two breaks of serve throughout the encounter.

Isner sent down 35 aces – including 17 in the final set – but was edged in the tie-break.

Escobedo will face Thomaz Bellucci in the semi-finals after the Brazilian eighth seed beat two-time runner-up Sam Querrey 6-4, 3-6, 6-3.