Memphis, TN (SportsNetwork.com) - No. 1 seed and two-time defending champion Kei Nishikori dropped a set but moved on at the Memphis Open and third-seeded American John Isner also won Wednesday to reach the quarterfinals.

Nishikori beat American qualifier Ryan Harrison 3-6, 6-3, 6-4 in just under two hours to keep alive his chances at a three-peat.

The U.S. Open runner-up will face another American qualifier, Austin Krajicek, who ousted No. 5 seed Ivo Karlovic 7-6 (7-4), 4-6, 6-4. Karlovic was last year's runner-up here to Nishikori.

Isner, the 2010 runner-up to fellow American Sam Querrey, defeated Ivan Dodig 6-4, 7-6 (7-5).

He will face Querrey, who eased past wild-card American Jared Donaldson 6-4, 6-1 on Wednesday.

The Memphis champion will earn $106,565.