Tennis star Novak Djokovic is back at the Australian Open, and the world’s number-one player is continuing his winning ways. 

Djokovic is looking for his 25th Grand Slam title and his 11th win in Melbourne. 

On Friday, Djokovic extended his winning streak at Melbourne Park to 31 in a straight-set victory over Tomas Martin Etcheverry.

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The victory wasn’t without controversy. 

As Djokovic prepared to serve for match point, a fan in the crowd had something to say. 

"Get vaccinated, mate," the fan yelled as the crowd murmured and booed. 

Djokovic stepped back before serving an ace to advance to the fourth round of the Australian Open. 

Djokovic is well known for his stance on the COVID-19 vaccine, which he refused to take, resulting in his deportation from Australia in 2022. 

Djokovic was initially granted an exemption to compete in the 2022 Australian Open. However, when he arrived in the country, he was told his exemption was not valid. 

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Djokovic was later deported from the country by Immigration Minister Alex Hawke. He returned to the tournament in 2023 and won his 10th Australian Open title. 

Last month, Djokovic sat down with "60 Minutes" and touched on the experience. 

"I was basically declared as a villain of the world," Djokovic said. "I had, basically, most of the world against me. I had that kind of experience on the tennis court with crowds that were maybe not cheering me on. But I never had this particular experience before in my life.

"I got the exemption, I got the permission to come into the country. So, of course, it escalated to the highest of highest levels globally."

Djokovic faces Frenchman Adrian Mannarino on Sunday and was pleased with his third-round performance. 

"I played better than I did in the first two rounds, so that’s a positive change, I guess," he said. "Starting to feel better game-wise and physically, as well. It’s positive signs."

Fox News’ Scott Thompson and the Associated Press contributed to this report.