Novak Djokovic has crashed out of his own tournament with Russia's Aslan Karatsev beating the world No.1 in a gruelling Serbia Open semi-final, that was the longest non-grand slam match of 2021.
Djokovic suffered his second successive shock exit on red clay, going down 7-5 4-6 6-4 in a three hour 25 minute marathon.
"It's definitely the most important victory of my career," Karatsev said.
"At the Australian Open in Melbourne, I felt like I was playing against a wall but this is a different surface and I was focused."
It followed Djokovic's defeat to Briton Dan Evans in the third round of the Monte Carlo Masters.
The Serb failed to convert a barrage of break points against Karatsev, who has made an extraordinary breakthrough this year after his big run to the last-four of the Australian Open - eventually losing to Djokovic.
In all, the Russian saved 23 of the 28 break points he faced on his way to the final of the ATP 250 event.
"It was a long, tough match (against a) tough opponent," Karatsev said in his post-match press conference.
"I stepped on the court to win.
"I was believing [in myself], and I said to myself that I would play every ball no matter what.
"I tried to keep this strategy that we spoke about with the coach.
"You have to fight for every ball, that was the key to success."
Djokovic felt it was a forgettable evening but he couldn't help but praise his conqueror.
"Hats off to Karatsev, he was bold and deserved to win," Djokovic told an online news conference.
"I was unlucky at times, it all came down to one or two shots but I had too many ups and downs throughout the match."
Karatsev will meet Matteo Berrettini in Sunday's final at Djokovic's tennis centre in downtown Belgrade by the Danube river.
The Italian second seed defeated Japan's Daniel Taro 6-1 6-7 (5-7) 6-0.