Andrey Rublev beat Novak Djokovic in the final of the Belgrade Open to deny the World No 1 crowning glory at home.
Rublev outlasted Djokovic 6-2, 6-7 (4), 6-0 at the ATP 250 clay-court event on Sunday to capture his third title of the season.
“It is big to play against you and share the court for the second time,” Rublev said to Djokovic during the trophy ceremony.
“I hope we have more battles. I feel so great here, it is a very nice city. It feels really special.”
The 24-year-old saved five set points in the second set to force a tie-break.
Though he was unable to prevent Djokovic from levelling the match, Rublev regrouped in the decider as he looked the fitter of the two to triumph after two hours and 29 minutes.
Djokovic was competing in his third event of the season.
The 34-year-old had lost in the quarter-finals in Dubai and suffered a shock second-round defeat against Alejandro Davidovich Fokina in Monte Carlo in the previous tournaments.
He battled past Laslo Djere, Miomir Kecmanovic and Karen Khachanov in three sets as he worked his way back into form.
However, the court time eventually caught up with the top seed against Rublev.
Carlos Alcaraz wins Barcelona Open
Carlos Alcaraz defeated mentor and eighth seed Pablo Carreno Busta 6-3, 6-2 to win the Barcelona Open on Sunday.
Alcaraz, who has now won three titles this season, climbed to No 9 on the rankings on Monday, making him the youngest player to crack the Top 10 since Rafael Nadal did it exactly 17 years ago after lifting his first Barcelona trophy.
“It means a lot. I’ve watched this tournament since I was a kid. I always wished to play in this tournament and of course to be able to win this tournament,” Alcaraz said.
“I’m really, really happy to be part of the [historic] Spanish list.”
Alcaraz, Rafael Nadal and Rublev lead the ATP Tour this season with three titles each.