Korea's Chung beats Djokovic 6-7 (4-7) 5-7 6-7 (3-7)
Djokovic struggling with elbow injury in fourth-round match
World number 97 Tennys Sandgren beats fifth seed Dominic Thiem
Halep beats Osaka to reach last eight
Federer wins in straight sets
Kerber and Keys also through
Djokovic 6-7 (4-7) 5-7 1-1 Chung*
Chung breaks back! He came from nowhere in that game, Djokovic just folded...
Agassi and Stepanek look absolutely distraught in the Serb's box.
Image source, AFP*Djokovic 6-7 (4-7) 5-7 1-0 Chung
Well, who needs luck when you can play precision backhand winners? Hyeon Chung powers one off his strings and down the line, leaving Novak Djokovic to just watch it on by.
Djokovic finds the net again, but this time there's no favourable bounce.
Break point.
David Law
Radio 5 live sports extra commentator at Melbourne Park
The crowd are aware Djokovic needs some help, some encouragement.
*Djokovic 6-7 (4-7) 5-7 1-0 Chung
Now Djokovic is getting the luck!
He cracks the tape, watches the ball loop into the air and a despairing Chung cannot reach it.
The crowd loves it.
Australia cricket captain Steve Smith is in the Rod Laver house.
Wonder what he's like at tennis? Unorthodox technique but highly efficient you'd think.
Image source, AFP*Djokovic 6-7 (4-7) 5-7 1-0 Chung
Chung lines up a forehand, only to hammer it into net.
Break point Djokovic. He takes it!
Mark Woodforde
Australian 12-time Grand Slam doubles champion on BBC Radio 5 live sports extra
That was a 30-shot plus rally and it took a lot out of Djokovic. Chung is barely breathing heavily.
Djokovic 6-7 (4-7) 5-7 0-0 Chung*
The clock reads two hours, 13 minutes. The scoreboard reads two sets to love in Chung's favour...
Djokovic is not about to back out just yet though, he battles to 15-30 but can't edge out the Korean in a mammoth 35-shot rally as Chung pulls back to 30-30.
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Djokovic 6-7 (4-7) 5-7 0-0 Chung*
Hyeon Chung to serve first in this third set.
Novak Djokovic gets the better of the opening point, watching a Chung forehand drift wide.
Djokovic 6-7 (4-7) 5-7 0-0 Chung*
Nineteen unforced errors in that second set for Novak Djokovic. Hyeon Chung made just six.
Mark Woodforde
Australian 12-time Grand Slam doubles champion on BBC Radio 5 live sports extra
Chung made a point of gesturing after winning that set - as though to say he's here and he means business.
*Djokovic 6-7 (4-7) 5-7 Chung
Novak Djokovic grunts into successive forehands, only to whip the next one against the tape.
That's the game and second set to Hyeon Chung.
Image source, AFP*Djokovic 6-7 (4-7) 5-6 Chung
Long from Djokovic, and this is set point for Chung...
*Djokovic 6-7 (4-7) 5-6 Chung
Novak Djokovic throws everything into a baseline return, but it bobbles awkwardly off his frame and beyond Hyeon Chung at the far end.
He recovers on the next point, that's 40-30, only to double fault for deuce.
*Djokovic 6-7 (4-7) 5-6 Chung
Again, Novak Djokovic finds himself serving to stay in the set.
A touch of angst among the Rod Laver Arena crowd, they're told to hush. It's getting late in Melbourne...
Hyeon Chung is still wide awake and firing, but he can't dance around a crosscourt Novak Djokovic backhand quickly enough to fire it on target.
The Serb backs it up with a powerful forehand winner.
Image source, EPADavid Law
Radio 5 live sports extra commentator at Melbourne Park
It's horrible seeing Djokovic hurting. You hope it's not getting worse. It's hard to read because it looked like he was going to retire.
It's human nature that when things are going badly that you feel the pain more.
*Djokovic 6-7 (4-7) 5-6 Chung
Magic from Hyeon Chung!
Somehow he reaches a crosscourt Novak Djokovic forehand that was drifting way wide of the court, almost doing the splits to coax a sliced response.
The Korean regains his feet, and picks out a fabulous winner.
He holds.
Djokovic 6-7 (4-7) 5-5 Chung*
Djokovic is smiling, but it's beaming bemusement from the six-time champion, who can't deal with Chung's depth off the opening service point.
The Serb rattles in a forehand to bring it back to 15-15, only to flop one long off his next return.
World number 97 Tennys Sandgren after beating fifth seed Dominic Thiem: "I don't know if this is a dream or not.
"He played some really great tennis especially in the fourth-set breaker. I knew I had to take my chances and knew he could outlast and outgrind me. I had to be aggressive and serve well.
"Thankfully it worked out in the end.
"Maybe guys aren't sure what to expect and don't know how I go about playing points. I am using that to my advantage and I am just trying to ride the wave."
Image source, AFP