Consider Novak Djokovic the sixth member of the Saja Boys ... 'cause the tennis superstar broke out a famous "KPop Demon Hunters" dance to celebrate his big US Open win on Tuesday!!
The Joker handled Taylor Fritz in four sets to advance to the semifinals ... and used the accomplishment to give a special shoutout to his daughter on her birthday.
To no surprise, the 38-year-old Serbian athlete's kid is one of the millions obsessed with the hit Netflix movie .