Isner reaches Houston quarters

Last year's runner-up John Isner was a hard- fought second-round winner Thursday at the U.S. Men's Clay Court Championship.

The fifth-seeded 6-foot-9 Isner outlasted fellow American Jack Sock 7-5, 6-7 (3-7), 7-6 (7-3) in 2 1/2 hours. The big-serving affair featured 28 aces, including 15 from the winner.

Isner lost to Argentine Juan Monaco in last year's Houston finale.

An upset came when Ruben Ramirez Hidalgo dismissed sixth-seeded fellow Spaniard Fernando Verdasco 6-3, 6-2 in 67 minutes.

Meanwhile, seventh-seeded Paolo Lorenzi topped fellow Italian Flavio Cipolla 7-6 (7-4), 6-1 and American wild card Rhyne Williams doused 6-foot-10 Croatian lucky loser Ivo Karlovic 6-4, 6-7 (5-7), 7-6 (7-3). Karlovic, who clubbed 28 aces in a losing effort on Day 4 and was a titlist here in 2007, replaced fourth-seeded American and 2010 runner-up Sam Querrey in the draw at River Oaks Country Club.

Rain washed away four scheduled second-round matches here on Wednesday.

The 2013 Houston champ will collect $82,300.