World number one Novak Djokovic won his opening match of the Adria Tour, as elite men's tennis returned for the first time since being suspended due to the coronavirus pandemic.
The Serb, 33, cruised past compatriot Viktor Troicki 4-1 4-1 in Belgrade in just 34 minutes.
Djokovic set up the tournament to help players get back to match fitness after several weeks of no competition.
The cross-Balkan event has a reduced match format and is open to spectators.
Djokovic, a 17-time Grand Slam singles champion, will next face Serbian Filip Krajinovic, 28, who lost to German world number seven Alexander Zverev, 23, 0-4 4-3 4-3 in the four-man group's other game.