Martin Klizan of Slovakia rallied to beat Italian lucky-loser Matteo Viola 4-6, 7-6 (6), 6-1 Tuesday in the first round of the Zagreb Indoors.

Croatia's Ivo Karlovic had 18 aces and upset seventh-seeded Bulgarian Grigor Dimitrov 7-6 (3), 7-6 (3). Dimitrov, who played his first career ATP singles final in Brisbane in January, did not concede a break but could not find the game to counter the strong-serving, towering Croat.

Grega Zemlja from Slovenia rallied from one set down to beat Ilija Bozoljac from Serbia 6-7 (5), 7-6 (4), 6-2. Somdev Devvarman of India also came back from a set and a break down to defeat two-time Zagreb finalist Michael Berrer, who retired because of fatigue when trailing 0-6, 7-6 (6), 4-1.

Also, Igor Sijsling of the Netherlands defeated Nikola Mektic of Croatia 6-4, 6-2, and Philipp Petzschner of Germany beat Mate Pavic of Croatia 7-5, 6-2.