NEW YORK -- John Isner, the highest-ranked American man, is out of the U.S. Open.

Mischa Zverev, the 23rd seed from Germany, ousted the No. 10 Isner 6-4, 6-3, 7-6 (5) to reach the fourth round.

Zverev never lost his serve, and broke the hard-serving Isner three times. Zverev also took advantage of 41 unforced errors by Isner, compared to just seven of his own.

Zverev, who reached the Australian open quarterfinals in January, has a chance to match that feat at Flushing Meadows if he can beat his next opponent and the last American man left, Sam Querrey.