BELGRADE, Serbia -- High-flying Serbian hero Novak Djokovic improved to a perfect 25-0 this year with a second-round victory Wednesday at the Serbia Open.

The top-seeded world No. 2 star cruised past Romanian qualifier Adrian Ungur 6-2, 6-3 in 68 minutes on the red clay at MGM Belgrade.

Djokovic is the reigning Australian Open champion and 2010 U.S. Open runner-up who already owns four titles this season. The super Serb captured his hometown event two years ago and led Serbia to its first-ever Davis Cup title here in Belgrade back in December.

The 23-year-old Djokovic's quarterfinal opponent on Friday will be Slovenian Blaz Kavcic.

Meanwhile, fourth-seeded Spaniard Albert Montanes came from behind to beat German Michael Berrer 3-6, 6-2, 6-2, Kavcic handled Brazil's Ricardo Mello 7-5, 6-3, and Spain's Feliciano Lopez topped on-the-mend Chilean slugger Fernando Gonzalez 6-4, 7-6 (7-4).

A wild card this week, Gonzalez had been sidelined since October after undergoing right hip surgery and hadn't won an ATP match in 11 months before prevailing in his first-round bout here on Tuesday.

Lopez will face his fellow Spaniard Montanes on Friday.

The 2011 Belgrade winner will pocket $96,800.