Hyeon Chung
Tennis - Australian Open - Rod Laver Arena, Melbourne, Australia, January 20, 2018. Hyeon Chung of South Korea reacts after winning against Alexander Zverev of Germany. Reuters / Thomas Peter

World No. 58 Hyeon Chung upset World No. 4 Alexander Zverev on Saturday in the third round of the 2018 Australian Open at the Rod Laver Arena. The 21-year-old from South Korea had beaten Zverev's older brother, Mischa, in the first round last Tuesday.

Zverev, one of the rising stars of tennis, couldn't keep his emotions in check during the 5-7, 7-6, 2-6, 6-3, 6-0 defeat to Chung. The young German fumed at the umpire for not turning on the lights in the fourth season. During the fifth set, after going down a double break, Zverev smashed his racket to the ground and received a code violation for racket abuse.

In November, Chung defeated Russia's Andrey Rublev to win the inaugural Next Generation ATP Finals. Chung avoided a clash with Zverev at the event since the German qualified for the senior ATP Finals in London. After Saturday's game, Zverev praised Chung's explosive game and compared the South Korean to Rafael Nadal.

“(Today was) similar (to last year's Nadal),” said Zverev, who lost to Nadal at the same juncture of last year's Australian Open. "You know, obviously in this one I was the favourite. In the one with Nadal, I wasn't. But game-wise this was not a bad match. He's 50-whatever in the world. But this was a top-10 level match from the start till the end of the fourth set, and for him until the end. You know, rankings sometimes lie. The way he was playing, it was definitely not whatever he is ranked," Zverev added via The Express.

Meanwhile, Chung thanked his training team after the biggest victory of his young career. "It was a really tough game against Alex Zverev. I'm just trying to play 100% and that was the key today. Training in Thailand, with my team -- they’re always with me in bad times, good times, and I’m so thankful. Today was a really tough match. I know he’s a really good player and we know how to play each other. I just tried to play 100 per cent," Chung said during the post-match interview.

The 2018 Australian Open rolls on Sunday with a fourth-round match pitting World No. 1 Rafael Nadal against Argentina's Diego Schwartzman. Chung will face Novak Djokovic in Monday's fourth-round match.