Fifth-seeded Martin Klizan of Slovakia came back from a set and a break down to beat Italian lucky-loser Matteo Viola 4-6 7-6 (8-6) 6-1 Tuesday in the first round of the Zagreb Indoors.

After winning the first set, Viola led 3-2 in the second when Klizan broke back. Klizan later wasted two set points before winning the set in a tiebreak.

Croatia’s Ivo Karlovic served 18 aces to upset seventh-seeded Bulgarian Grigor Dimitrov in straight sets and two tie breaks, 7-6 (7-3) 7-6 (7-3).

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.

“This match was tough,” Dimitrov said. “I have practiced with Ivo quite a few times and I knew what to expect.”

Karlovic, who had not previously managed a single victory this season, said “I finally won.”

He added: “Home crowd helped… I always feel good here.”

Grega Zemlja from Slovenia rallied from one set down to beat Ilija Bozoljac from Serbia 6-7 (7-5) 7-6 (7-4) 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 (8-6) 4-1.

Also, Igor Sijsling of the Netherlands defeated Nikola Mektic of Croatia 6-4 6-2, Philipp Petzschner of Germany beat Mate Pavic of Croatia 7-5 6-2, and Lukas Rosol of the Czech Republic beat another Croat, Filip Veger, 6-2 6-4.

AP