Australian Open: Novak Djokovic crashes out to South Korean Hyeon Chung

An injury-ravaged Novak Djokovic is out of the Australian Open, the six-time champion losing in straight sets to South Korean prodigy Hyeon Chung in the fourth round.

The 14th-seeded Serb needed a medical timeout for treatment of his injured elbow and was in obvious discomfort throughout as Chung stormed to a 7-6 (7-4) 7-5 7-6 (7-3) victory on Rod Laver Arena.

It continues a giant-killing run for world No 58 Chung, who defeated fourth seed Alexander Zverev on Saturday and his older brother, 32nd seed Mischa, in the opening round.

Djokovic must have felt like he was playing a younger - and fitter - version of himself throughout their three-hour, 21-minute clash.

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The 21-year-old Chung bore an uncanny resemblance to his childhood idol with his speed, athleticism and freakish retrieval skills.

Coming off a six-month layoff, the longest of his career, Djokovic's health had been questioned throughout the tournament and his troublesome right elbow appeared far from healed.

Again wearing a full compression sleeve on his arm, Djokovic sent down four straight double-faults in falling to a 4-0 deficit in the opening set.

The 12-time grand slam winner fought back to force a tiebreak but was clearly in pain when at full stretch and called for the trainer in between sets.

Chung continued to play inspired tennis, leaving Djokovic down two sets to love at Melbourne Park for the first time since his fourth-round loss to eventual champion Roger Federer in 2007.

Interviewed ahead of the tournament, Djokovic insisted he had not had surgery on his elbow but was tight-lipped on the exact nature of his injury and how he was managing his pain.

"Djokovic in trouble," former Wimbledon champion Pat Cash posted on Twitter as Chung pressed his advantage.

"Elbow seems to be bothering him and he's not even running to some balls. Injuries seems to be weighing on him physically and mentally now.

"Sad to see the six time champ still struggle with injuries after six months of rest and rehab."

While clearly struggling, the Serbian refused to give up.

Serving at 4-4 in the third set, Djokovic attempted to rally the crowd in his favour after seizing on a telegraphed drop shot by Chung and hitting a slice backhand winner.

But Chung would not be denied, prompting superlatives from former world No.1 Jim Courier as he capped a gruelling tiebreak rally with an outrageous cross-court forehand winner.

"I cannot believe what I'm seeing," Courier said on the Seven Network.

"I cannot believe how good this kid is."

Chung will face world No 97 Tennys Sandgren in the quarter-finals on Wednesday after the aptly-named American's shock defeat of Austrian fifth seed Dominic Thiem.


Earlier, Tennessee-born, tennis-loving Tennys Sandgren caused one of the biggest upsets at the Australian Open, knocking out fifth-seeded Dominic Thiem to advance to the quarterfinals.

Previously winless at grand slams, the aptly-named American continued his astonishing run at Melbourne Park with a 6-2 4-6 7-6 (7-4) 6-7 (7-9) 6-3 victory in three hours and 54 minutes.

His reward will be a final-eight showdown with either six-time champion Novak Djokovic or South Korean rising star Hyeon Chung.

"I don't know if this is a dream or not," Sandgren said.

"All of you guys are here and I'm not in my underwear, so maybe it's not a dream.

"This is my fifth Australian Open; I've lost in (qualifiers) four years.

"This is my first main draw at the Australian Open and now I'm in the quarter- finals."

Sandgren arrived at Melbourne Park having only twice made the main draw of a major from 15 attempts.

The world No 97 scored a US Tennis Association wildcard entry to last year's French Open.

He was then bumped up to the main draw of the US Open when Japan's Yoshihito Nishioka withdrew through injury.

Both times, he was beaten in the first round.

Sandgren has now seen off two of the top men's seeds, having defeated an injury- hampered Stan Wawrinka in the second round.

He is just the second man in 20 years to make the quarter-finals of the Australian Open in his first main-draw appearance.

"He's a heck of a player, so I knew I had to come out and play aggressive and take my chances and serve well," Sandgren said of Thiem.

"Thankfully, it worked out in the end."

 - AAP