Fifth-seeded Martin Klizan was among Tuesday's opening-round winners, while seventh seed Grigor Dimitrov was an upset victim at the Zagreb Indoors tennis event.
The rising Slovakian Klizan came from behind to beat Italian qualifier Matteo Viola 4-6, 7-6 (8-6), 6-1, while the Bulgarian Dimitrov lost to 6-foot-10 Croat Ivo Karlovic 7-6 (7-3), 7-6 (7-3) at Dom Sportova. The massive-serving Karlovic fired up 18 aces and was not broken by Dimitrov, who also held his serve throughout en route to defeat.
Slovenian Grega Zemlja overcame Serbian qualifier Ilija Bozoljac 6-7 (5-7), 7-6 (7-4), 6-2 and is rewarded with a second-round match against top- seeded Croatian crowd favorite and two-time Zagreb champion Marin Cilic.
Also on Day 1, Czech slugger Lukas Rosol dismissed Croatian lucky-loser Filip Veger, 6-2, 6-4; Indian Somdev Devvarman saved a match point before getting past German and two-time Zagreb runner-up Michael Berrer 0-6, 7-6 (8-6), 4-1, retired; Slovenian Blaz Kavcic overcame Slovenian Aljaz Bedene 6-7 (5-7), 6-3, 6-3; Dutchman Igor Sijsling whipped Croatian wild card Nikola Mektic 6-4, 6-2; and German qualifier Philipp Petzschner topped Croatian wild card Mate Pavic 7-5, 6-2. Berrer succumbed to fatigue and exhaustion on Tuesday.
Russian Mikhail Youzhny defeated Slovak Lukas Lacko in last year's Zagreb finale. A third-seeded Youzhny, who enjoyed an opening-round bye this week, will battle Sijsling on Wednesday.