WASHINGTON (AP) Ivo Karlovic hit 26 aces and saved all four break points he faced while beating sixth-seeded Jack Sock 7-6 (4), 7-6 (6) on Friday at the Citi Open to reach the hard-court tournament's semifinals for the first time since 2007.
Sock had a chance to force a third set, holding a set point at 6-5 in the second tiebreaker. But the 13th-seeded Karlovic erased that with a 133 mph ace, then delivered a 130 mph service winner to get to match point and won when Sock's forehand clipped the net tape and sailed wide.
Sock was one of four U.S. men in the quarterfinals in Washington, the first time that many made it that far at the event since 2003.
Karlovic's next opponent will be an American, either No. 1-seeded John Isner or No. 5 Steve Johnson.