By MATT WINKELJOHN
ATLANTA (AP) - Two-time defending champion John Isner beat Radek Stepanek 7-6 (3), 7-6 (7) on Thursday night in his opening match in the Atlanta Open.
The top-seeded Isner has reached the final four of the last five years, winning the last two after losing to Mardy Fish in 2010 and 2011. Isner is 12-1 in tiebreakers in Atlanta since 2012.
Isner's booming serve was potent, with the 6-foot-10 former University of Georgia player ripping 33 aces to three for Stepanek. Yet the world's No. 19-ranked player was on the ropes a couple times against the 144th-ranked Stepanek in the final match of a day that saw three seeded players drop out.
Ukrainian qualifier Denis Kudla upset third-seeded Jack Sock 7-6 (6), 6-3, and No. 6 Steve Johnson and No. 8 Benjamin Becker also tumbled out. Israel's Dudi Sela, who fell in the 2014 final to Isner, beat Becker, from Germany, 7-5, 6-3, and Ricardis Berankis of Lithuania rolled past Johnson 6-4, 6-2.
Isner will face Berankis on Friday in the quarterfinals.
Copyright 2015 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.