Vienna: World Number one Novak Djokovic tops the list of six top ten ATP players in action in Vienna this week.
The Serbian is back to the Austrian tournament for the first time since 2007 when he lifted the trophy.
Djokovic passed a tough test in his first match, as he faced a good friend and a countryman Filip Krajinovic.
Djokovic dropped serve twice in the first set and was forced to save a set point at 5-6, before coming back to earn his place in the second round.
He will next face Borna Coric for a place in the quarter-finals.
Grigor Dimitrov outlasted Karen Khachnov in their first-ever meeting.
An even first set ended in a tie-breaker. It could have gone either way but Dimitrov held his nerve to take the opener 8-6.
The Bulgarian broke Khachanov serve to go up 3-0 in the second set.
And then went on to break him again to make it 5-1.
The Russian immediately broke back but it was too late for him to get back into the match.
Home favourite and defending champion Dominic Thiem was made to work hard in his opening match against 23-year old Ukrainian Vitaliy Sachko.
World number 529 broke the second seed on four occasions on his tour-level debut.
But the US Open champion raised his level to close out the match 6-4 7-5.
Thiem will resume his title defence in a match against Chile's Cristian Garin who defeated three-time Grand Slam winner Stan Wawrkina.
