MEMPHIS, Tenn. (AP) - Ivo Karlovic of Croatia used his powerful serve in beating American Jack Sock 7-6 (4), 6-7 (3), 6-3 on Friday night in the quarterfinals of the U.S. National Indoor Tennis Championships.

Karlovic, with five career titles, served up 16 aces in knocking the 21-year-old Sock out of his second quarterfinal this year. Karlovic needed 2 hours, 25 minutes, and he finally got the edge in the match by breaking Sock to go up 2-1 in the third. Karlovic converted only one break point after failing on his first 10 chances.

He will play fourth-seeded Lu Yen-Hsun of Taiwan on Saturday. Lu beat American qualifier Alex Kuznetsov 6-1, 6-4 earlier Friday.

Michael Russell upset third-seeded Lleyton Hewitt of Australia 6-3, 7-6 (6) to reach his third career ATP Tour semifinal. Russell will play defending champion Kei Nishikori, a 3-6, 6-3, 6-2 winner over Russia's Alex Bogomolov Jr

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