Two-time champion Djokovic eases into Belgrade semi-finals
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Djokovic, the 2009 and 2011 champion at the event which is played at a venue which carries his name, will face either Russia's Aslan Karatsev or Gianluca Mager of Italy for a place in the final.
In their first meeting, Djokovic broke his 21-year-old opponent's first service game and repeated the feat for a 5-1 lead in the opener.
His only blip was when he was broken as he served for the match at 5-2 in the second set.
However, it was a brief respite for world number 47 Kecmanovic who handed back the break in the next game allowing the top seed to complete a 75-minute win.
Djokovic, who captured an 18th Grand Slam title in Australia in February, opened his clay court campaign in Monaco last week where he suffered a surprise last-16 loss to Britain's Dan Evans.