World number one Novak Djokovic was brought to tears after he bowed out of his Adria Tour with victory over German Alexander Zverev in front of home fans.
The 4-0 1-4 4-2 win sent fellow Serb Filip Krajinovic into the final.
Djokovic's event - the first elite men's tennis since it was suspended by coronavirus - attracted 4,000 fans.
"I am just overwhelmed by emotion because this reminds me of my childhood," he said as the Belgrade crowd gave him a standing ovation.
"It's been an emotional few days and I want to thank everyone who made this possible. The important thing after this match is that we have one of our own in the final. I love you all and thank you so much for turning up."
Krajinovic later lost to Austrian world number three Dominic Thiem 4-3 2-4 4-2 in the final.
Djokovic, 33, set up the tournament to help players get back to match fitness after several weeks without competition.
Players were split into two groups of eight and played each other in a round-robin format, with the two group leaders competing in a final later on Sunday.
Players needed four games to win a set, with a tie-break at 3-3, and matches were best of three sets.
The next leg takes place in Zadar, Croatia, from 20 June but the tournament's third leg, scheduled for Montenegro, has been cancelled because Serbian citizens are banned from entering the country amid the coronavirus pandemic.
The final event is in Bosnia-Herzegovina in July.
Several top 10 players are also competing in the Ultimate Tennis Showdown, an event created by Serena Williams' coach Patrick Mouratoglou in Nice, France.
Matches are being held without spectators.
Italian world number eight Matteo Berrettini defeated Dustin Brown, Spain's Feliciano Lopez beat France's Lucas Pouille, with Belgian world number 10 David Goffin losing to Richard Gasquet.
The regular ATP Tour is suspended until at least 31 July.