Novak Djokovic had to work hard to defeat Alexei Popyrin at the Australian Open. Popyrin made things interesting, but Djokovic narrowly emerged victorious. ESPN reports that during the match, Djokovic challenged a heckler.

The incident seemingly motivated Djokovic, who started finding his form once again after calling out the heckler.

“Djokovic also challenged a heckler to ‘say that to my face' during the fourth set. At 2-2, Djokovic paused, walked to the back of the court and yelled at the spectator before winning the next three games,” ESPN reported.

Djokovic is a superstar but admitted that he's been struggling at times in recent matches, via ESPN as well.

“I haven't been playing my best, but still trying to find form,” Djokovic said. “Particularly in the early rounds, you play players that have nothing to lose. They come out on center court to play their best tennis.”

Novak Djokovic still finding ways to win

It should be noted that Djokovic has been dealing with a wrist injury. However, the superstar previously shut down concerns in reference to the injury.

“I knew that probably, [I am] not going to be at 100 per cent physically, emotionally, mentally game-wise in the opening week of a season. Neither did I expect that,” Djokovic said previously, via ATP Tour. “I was not on my level, but it was just one of these days where I didn't feel my best on the court, and [my] opponent played very well. That's all I can say.”

Perhaps the injury has played a role in Djokovic's inconsistency. He still displayed the ability to perform at an elite level toward the end of the match against Popyrin.

As for Novak Djokovic and the fans, he recently made his feelings clear on an Australian Open new rule. Fans are now allowed to enter the main area, and the fans have frustrated Djokovic at times.

“I did not know about that new policy or new rule,” Djokovic said, via Liam O'Loughlin of Wide World of Sports. “I understand the motive behind it is to enhance and improve the experience for fans, right? We do play for fans. We want fans to have a great, thrilling experience. It's hard, I must say. I understand that and I support it to some extent, but at the same time all my career, all my life I've been used to some kind of atmosphere.”

The rowdy fans led to Djokovic screaming, “shut the f**k up” during a recent match. Although Djokovic understands the new rule, he is still clearly willing to call hecklers out.