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) 5-5 Chung*
Now the pressure is on Djokovic.
Chung just tickles a backhand over the net, it throws Djokovic off slightly and he can't muster the composure to muster a meaningful response.
That's better. Punchy groundstrokes leading to a ferocious forehand winner, and Djokovic holds.
*Djokovic 6-7 (4-7) 4-5 Chung
Frustrating for Hyeon Chung, superb winner one minute, disappointing unforced error the next.
He drops two points as Novak Djokovic goes 40-15 up.
But then it's the six-time champion's turn to drop a loose backhand long.
*Djokovic 6-7 (4-7) 4-5 Chung
Approaching the two-hour mark out on Rod Laver Arena, and it's Novak Djokovic serving to stay in the second set.
The Serb rattles off a ferocious ace from mid-court - have that - but has to stretch to reach a Chung backhand and the Korean backs it up with a well-placed winner.
*Djokovic 6-7 (4-7) 4-5 Chung
Chung gets the better of a lengthy exchange and then powers in a punishing first serve to go 30-15 up.
He's got some serious pace on the backhand side too, and Djokovic can't muster up enough speed to force it back over the net.
Chung holds.
Djokovic 6-7 (4-7) 4-4 Chung*
So the winner of this last-16 meeting will play Tennys Sandgren in the quarter-finals. If ever there was a man born to play the sport...
Djokovic 6-7 (4-7) 4-4 Chung*
Hyeon Chung had a moment like this in the first set, going 4-0 up but watching Novak Djokovic fight back before winning the tie-break.
He's given up a break in the second set, and now Djokovic has the chance to level up.
The Serb isn't in the mood for hanging around, storming to 30-0. But that's too much spring off the strings and the backhand drifts long.
The only blemish only Djokovic's service game.
Thiem 2-6 6-4 6-7 (4-7) 7-6 (9-7) 3-6 Sandgren
Fifth seed Dominic Thiem has been knocked out of the Australian Open by world number 97 Tennys Sandgren!
A nerveless service game from the American. What an upset.
Image source, AFP*Djokovic 6-7 (4-7) 3-4 Chung
Chung wraps a forehand into the net. Djokovic breaks back.
Djokovic 6-7 (4-7) 2-4 Chung*
A touch of frustration in the face of Chung, as he flops a backhand beyond the baseline.
A steely glare at the ball boy through those science goggle-esque specs. It's Djokovic with two break points.
Thiem 2-6 6-4 6-7 (4-7) 7-6 (9-7) 3-4 Sandgren*
World number 97 Tennys Sandgren has broken serve in the decider against fifth seed Dominic Thiem! He roars to his fans in the crowd who all stand and applaud.
We could be in for a big shock on the Hisense Arena.
Russell Fuller
BBC tennis correspondent at Melbourne Park
Djokovic still has an enormous presence and aura to someone like Chung who looked up to him when he was growing up.
He is still capable of turning this around but certainly the body language and facial expressions suggest otherwise.
Image source, EPADjokovic 6-7 (4-7) 2-4 Chung*
Djokovic saves with another display of subtlety off his backhand side. Chung just can't reach it.
The Serb wrong-foots the 21-year-old with a dipping forehand to hold.
*Djokovic 6-7 (4-7) 1-4 Chung
He can't get the next one right, though. Not enough on the half-volley, and then batting a straightforward forehand on the run wide.
Break point Chung.
*Djokovic 6-7 (4-7) 1-4 Chung
Djokovic with hands as soft as, well... a six-time Australian Open champion.
The's delicate, deft, delightful. Slicing narrowly over the net from deep court.
Chung rallies to deuce.
*Djokovic 6-7 (4-7) 1-4 Chung
Chung has Djokovic rooted to the spot with a ferocious display from the baseline.
The Korean is loose and long off a high-bouncing Djokovic serve though, and then loops a backhand into the tramlines - 30-30.
*Djokovic 6-7 (4-7) 1-4 Chung
Chung has made 22 winners to Djokovic's 16 today. He's getting his first serve in more regularly and winning more points off it, too...
It's Djokovic to serve though. He challenges a wide call, but the call was good - 0-15.
Russell Fuller
BBC tennis correspondent at Melbourne Park
That last shot was a shot of a man who has no interest in the outcome of this match.
Image source, Getty Images*Djokovic 6-7 (4-7) 1-4 Chung
That's the hold for Hyeon Chung.
Novak Djokovic is walking to his chair, towel around his neck, penny for your thoughts...
Djokovic 6-7 (4-7) 1-3 Chung*
Chung is forced back way behind the baseline by some deep Djokovic strokes, but he keeps forcing it back and eventually the Serb cracks, rattling the net.
He steams into a 40-0 lead with a well-timed smash.
Djokovic 6-7 (4-7) 1-3 Chung*
Djokovic turns this game back in his favour with a punchy display of serving, and he holds.