VIENNA (AP) Ivo Karlovic hit 16 aces to beat last year's runner-up Steve Johnson 7-6 (5), 6-3 Monday on the opening day of the Erste Bank Open.
The eighth-seeded Croat saved six break points as he held serve throughout and converted the only chance he got on the American's serve at 3-2 in the second set.
Karlovic next plays qualifier Damir Dzumhur of Bosnia-Herzegovina, who defeated the 43rd-ranked Nicolas Almagro of Spain 6-3, 5-7, 6-0.
Also, John Isner held off all seven break points against his serve as he rallied to defeat Jan-Lennard Struff of Germany 6-7 (1), 6-3, 6-4.
Karen Khachanov beat Andreas Seppi 6-4, 6-4 to set up a match against second-seeded Tomas Berdych or Nikoloz Basilashvili of Georgia.
Andy Murray is the top-seeded player at the Austrian indoor event.