Novak Djokovic made a winning return at his own Adria Tour event in Belgrade, only to be upstaged by a ball boy.

The world No.1 was everywhere on the opening day of singles action at the exhibition series.

It is his eponymous foundation which supports the exhibition series, the opening weekend of which takes place at the tennis academy which bears his name and he was competing in the Novak Group.

The 33-year-old was well on the way to beating Victor Troicki in his first match of the day when his fellow Serb handed over his racket to a young court-side helper, who returned twice from a Djokovic serve before hitting a forehand winner at the net.

Troicki summoned the boy over and patted his shoulder, the latest example of the event’s lack of social distancing, which allowed fans to sit side by side in the stands, attendants to collect towels and players to hug and shake hands.

The moment of levity done, Djokovic broke to love to complete a 4-1, 4-1 win.

“I really enjoyed myself out there,” Djokovic said in a courtside interview.

“Viktor started well but he seemed to have lost his momentum after the opening few games and in this format the match can be over pretty quickly.

“Once again I want to thank every player who turned up and all the fans who flocked in, their presence has made this weekend a memorable one.’

Grigor Dimitrov had earlier beaten Dusan Lajovic 4-3, 3-4, 4-1 in a high-quality contest, while Damir Dzumhur had to retire with injury early in his match with Dominic Thiem.

Alexander Zverev bested Filip Krajinovic in a tie-break to settle a final-set decider.

Nikola Milojevic was called up as Dzumhur’s replacement and will line up against Dimitrov in the evening session.

Meanwhile, the third event of the Adria Tour, due to take place in Montenegro at the end of the month, has been cancelled by local organisers.