Novak Djokovic made a triumphant return to tennis on his own Adria Tour event in Belgrade only to be upstaged by a ball boy.
The world No 1 featured prominently throughout the opening day of the exhibition series, which is being supported by his own foundation.
The 17-time Grand Slam champion featured in the Novak Group against compatriot Victor Troicki.
But just as it appeared as if the 33-year-old would secure a routine victory, Troicki handed over his racket to a young court-side helper, who swiftly returned twice from Djokovic's serve before incredibly 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. 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.
The evening session featured a shock result as Dzumhur's replacement, Serbia's world No 145 Nikola Milojevic, beat 19th-ranked Dimitrov of Bulgaria 4-1 4-3.
Lajovic almost caused another upset against Austria's Dominic Thiem, but the world No 3 came from a match point down to win 1-4 4-1 4-3 (8-6)
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.
PA contributed to this report
