John Isner posted a quarterfinal victory against defending champion Ryan Sweeting on Friday at the U.S. Men's Clay Court Championship.

The No. 2 seed Isner won two tiebreakers to take a 7-6 (7-1), 7-6 (7-4) win over Sweeting in an All-American confrontation at River Oaks Country Club.

Isner fired 11 aces and saved all six break points he faced. It was Isner's second straight win over Sweeting this year.

Isner will face third-seeded Spaniard Feliciano Lopez in the semifinals after he led, 6-4, 2-2, before Argentine Carlos Berlocq retired with a lower leg injury.

Michael Russell, a 33-year-old Houston resident who defeated No. 1 seed Mardy Fish on Thursday, reached the semifinals with a 6-1, 5-7, 6-3 win over 19- year-old fellow countryman Ryan Harrison.

Russell will tangle with fourth-seeded Argentine Juan Monaco, who reached his third semifinal of the season by defeating fifth-seeded South African Kevin Anderson, 7-6 (7-4), 7-5.

The winner of this $522,000 tournament will collect $71,900.