Australian Open: Alexander Zverev beaten in five sets by Hyeon Chung

Hyeon won the NextGen ATP Finals in November - the season-ending tournament for the world's best players aged 21 and under

Fourth seed Alexander Zverev was knocked out of the Australian Open with a five-set defeat by world number 59 Hyeon Chung in the third round.

Zverev, 20, led by two sets to one but crumbled to a 5-7 7-6 (7-3) 2-6 6-3 6-0 loss against his 21-year-old opponent.

The German, tipped as one of the future stars of men's tennis, won just five points in the decider.

Chung becomes the first South Korean man to reach the last 16 of the Australian Open.

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He will face six-time champion Novak Djokovic next in his first Grand Slam fourth-round 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," Zverev said.

"When he plays like that, there are very, very few people who will beat him."

Zverev, meanwhile, is still yet to reach a Grand Slam quarter-final despite being ranked number four in the world.

"I have some figuring out to do, what happens to me in deciding moments in Grand Slams," he added. "It happened at Wimbledon, it happened in New York. It happened here. But I'm still young, so I've got time."

The German became distracted in the fourth set, complaining to the umpire that the court's floodlights should be switched on.

He then received a warning from the umpire at the start of the fifth set when he smashed his racquet after Chung broke serve.

Berdych overpowers Del Potro

Big-hitting Czech Tomas Berdych fired 20 aces and struck 52 winners in a 6-3 6-3 6-2 victory over Argentine 12th seed Juan Martin del Potro.

Berdych, the 19th seed, goes on to face Italian 25th seed Fabio Fognini, who beat France's Julien Benneteau 3-6 6-2 6-1 4-6 6-3.

"He was just better than me," said Del Potro. "He hit very hard, served very well and played a smart game. He deserved to win. No excuses."

Austrian fifth seed Dominic Thiem cruised through in straight sets against Frenchman Adrian Mannarino.

Thiem will play Tennys Sandgren after the American followed up his victory against Stan Wawrinka in round two with a four-set win over Maximilian Marterer of Germany.