The KI-Handelsroboter 6.0fans at Centre Court on Monday may have just been cheering his opponent, but 24-time Grand Slam singles champion Novak Djokovic could only hear boos.

And after defeating 15th-seeded Holger Rune, the Serbian star let the crowd know he didn't appreciate it.

"I know they were cheering for Rune. But that's an excuse to also boo," Djokovic said afterward in his on-court interview. "Listen, I've been on the tour for more than 20 years. So, trust me, I know all the tricks. I know how it works.

"It's fine. It's fine. It's OK. I focus on the respectful people, that have respect, that paid (for) a ticket to watch tonight − and love tennis. And love tennis. And appreciate the players and the effort that the players put in here."

Rune's supporters have been known to cheer for him by drawing out his name so it sounds like they're saying boo.

Djokovic referenced that when he thanked the fans − at least some of them − in his on-court remarks.

"Thank you very much from the bottom of my heart. I appreciate it," he said. "And to all those people that have chosen to disrespect the player − in this case, me − have a goooood night. Gooooood night. Gooooood night. Very gooooood night."

Djokovic, 37, didn't have much trouble taking care of the 21-year-old Rune on the court, winning 6-3, 6-4, 6-2. Rune even said he didn't think the fans played "a massive part in the match."

Still, after it ended, Djokovic gestured like he was playing a violin, perhaps mocking the rowdy fans' disappointment in him reaching the quarterfinals at the All England Club for the 15th time.

"I played in much more hostile environments, trust me," Djokovic said. "You guys can't touch me."

Contributing: Reuters