Novak Djokovic erupts during his three-set loss to Aslan Karatsev of Russia at the Serbia Open tennis tournament in Belgrade, Serbia. EPA-EFE/ANDREJ CUKICAslan Karatsev fought off 23 of 28 break points he faced upsetting world No. 1 Novak Djokovic on his home court at the Serbia Open tennis tournament in Belgrade, Serbia. EPA-EFE/ANDREJ CUKICThe three-hour, 25-minute battle was the longest ATP Tour match of the 2021 season. EPA-EFE/ANDREJ CUKIC “I wasn’t thinking in those moments. There was no time to think!” said Aslan Karatsev of facing break-point pressure against Novak Djokovic scoring the biggest win of his career with a 7-5, 4-6, 6-4 stunner. EPA-EFE/ANDREJ CUKIC Novak Djokovic unleashes a primal scream during his three-set loss to Aslan Karatsev of Russia at the Serbia Open tennis tournament in Belgrade, Serbia. EPA-EFE/ANDREJ CUKICAslan Karatsev of Russia (R) shakes hands with Novak Djokovic of Serbia after powering into his first ATP clay-court final in Belgrade. EPA-EFE/ANDREJ CUKICTaro Daniel of Japan in action against Matteo Berrettini of Italy during their semi final match of the Serbia Open tennis tournament in Belgrade, Serbia, 24 April 2021. EPA-EFE/ANDREJ CUKICMatteo Berrettini of Italy reacts during his semi final match against Taro Daniel of Japan at the Serbia Open tennis tournament in Belgrade, Serbia, 24 April 2021. EPA-EFE/ANDREJ CUKIC