ATLANTA (AP) Ukrainian qualifier Denis Kudla upset third-seeded Jack Sock 7-6 (6), 6-3 on Thursday in the Atlanta Open, and No. 6 Steve Johnson and No. 8 Benjamin Becker also tumbled out.
Sock, an American ranked No. 35 in the world, battled in the first set before falling quickly in the second when his service game all but abandoned him on the super-heated court at Atlantic Station.
In the final second set, Kudla won 7 of 14 points on Sock's first serve was 5 of 12 on second serves while breaking the American's service game twice. Sock entered the match 17-8 in ATP matches this season, but struggled in the high heat and humidity.
The 94th-ranked Kudla reached the round of 16 at Wimbledon a month ago.
Israel's Dudi Sela, who fell in the 2014 final to John Isner, beat Becker, from Germany, 7-5, 6-3, and Ricardis Berankis of Lithuania rolled past Johnson 6-4, 6-2.
Isner, the top seed and a local favorite after playing at the University of Georgia, opened his title defense Thursday night against Radek Stepanek of the Czech Republic.