John Isner enters Houston semis

Juan Monaco of Argentina in action against USA’s Sam Querrey in the US Men’s Clay Court Championships quarter-finals in Houston, Texas (USA), on Friday. Monaco won 6-4, 6-4. (Photo: AP)

Top seed and former title-holder John Isner downed Chung Hyeon 7-6 (7/5), 6-4 on Friday to book a semi-final clash with defending champion Jack Sock at the ATP claycourt tournament in Houston on Friday.

Isner, who lifted the trophy in 2013, saved all seven break points he against the rising South Korean star, firing 14 aces and winning 58 per cent of his second serve points.

The US veteran was solid when it mattered most against the 19-year-old Chung, voted last year’s Most Improved Player by his peers.

“That one game in the first set, I was down four break points,” Isner said.

“Serving at 4-3 (in the second), I was down three break points and I had to hit a stab volley on one of them. That was huge. He played a good return game.”

Although he pulled off the win, Isner said he expected to see Chung continue to rise.

“He’s only going to get better, he’s only going to get stronger, he’s going to make all his shots better,” Isner said.

“At 19 years old, he’s got such an incredible ceiling right now.”

Isner set up a clash with another young standout in Sock, who defeated seventh-seeded Cypriot Marcos Baghdatis 6-4, 6-4.

Sock, seeded fourth, converted two of his eight break point opportunities and that was enough to extend his Houston winning streak to seven matches.

Former champion Juan Monaco of Argentina ousted fifth-seeded American Sam Querrey 6-4, 6-4 to book a semi-final against third-seeded Spaniard Feliciano Lopez, a 6-2, 6-3 winner over American Tim Smyczek.

“Every match that I play here, especially on center court, I feel great, I feel confident,” said Monaco, who won in Houston in 2012.

Monaco, now ranked 148th in the world, is in his first semifinal in more than a year. He will face a tough task against Lopez, who leads their career head-to-head 4-2.