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.

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.

Earlier, Bulgaria's Grigor Dimitrov, 29, battled to a 4-1 3-4 4-1 victory over Serbia's Dusan Lajovic, 29.

In their group's second game, Bosnia's Damir Dzumhur, 28, retired through injury at 2-0 down in the opening set against world number three Dominic Thiem, 26, of Austria. Serbian world number 145 Nikola Milojevic will replace Dzumhur in the evening session.

The regular ATP Tour is suspended until at least 31 July.

How does the Adria Tour tournament work?

Meanwhile, rain has washed out the opening day of the Ultimate Tennis Showdown in Nice, France, which is set to feature several top 10 players including Stefanos Tsitsipas, Matteo Berrettini and David Goffin,

Matches scheduled for Saturday will be played on Monday while matches set for Sunday remain unchanged.

The tournament was created by Serena Williams' coach Patrick Mouratoglou, at his namesake tennis academy in Southern France.