A Djokovic forehand is called out, thumping one beyond Chung... but that flirts with the line, just clipping the outside of the white to stay in.

Chung takes the next point with a fiery backhand, and with that the first set!

Image source, getty

From the sublime, to sloppy... Djokovic goes long from the baseline, and is even further off target with the next point.

Three set points for Chung.

It's also a thrilling tie-break over on Hisense Arena. Dominic Thiem led 4-1, needing to win this breaker to force a decider, but has been pegged back. He's just fought off a match point against Tennys Sandgren.

Image source, EPA

There we go - that's the Novak Djokovic who won six Australian Opens, getting the better of a 26-shot rally by pinning Chung in the corner and then volleying into the space left behind at full stretch. Wonderful.

Chung leads 4-3.

Anything you can do... Djokovic shows off his own volleying repertoire with impressively soft hands to drop a slice just over the tape on the run.

But then double faults. 3-2 Chung.

Djokovic goes long off the Chung serve, and the Korean then slips a lovely slice volley out of the Serb's reach to go 2-1 up.

Image source, EPA

Magnificent from Djokovic, an exquisite forehand winner down the line - 1-0.

Mark Woodforde
Australian 12-time Grand Slam doubles champion on BBC Radio 5 live sports extra

It looks like Djokovic is starting to find his range. The points that are missing are not missing by much.

Djokovic has Chung scuttling across court like the final few levels of the bleep test.

But the Korean passes with flying colours.

He holds, and it'll be a tie-break.

Tennys Sandgren has forced a tie-break against Dominic Thiem. If the world number 97 wins it he'll knock out the fifth seed.

There's not really been any rhythm to this match so far. Chung stormed into a lead, Djokovic fought back, but it's been bitty and wayward since then.

It's the six-time champion in the ascendancy at the moment, though.

Chung has other ideas, working his man wide and taking the point with a smash at the second attempt - 30-15.

Ouchy. The Korean is furious, he rattles a forehand off the frame and screams in frustration.

Djokovic responds with his own roar, but this one's relief. He moves to advantage, and then grunts his way into a punchy forehand to hold serve.

"Come onnnnn," is the cry.

Long from Novak Djokovic, and that gives Chung the chance to break.

Hyeon Chung had a 4-0 lead... but he's facing the six-time champion, who appears to have just warmed up.

Novak Djokovic picks his spot with a half volley from close range, but Chung reaches it - only to then find the net.

Djokovic smashes, stumbles, recovers his footing and is able to just about coax a winner at the net to make it 30-30.

Nerves of steel Tennys Sandgren. He must hold to prevent Dominic Thiem forcing a decider and the American does just that.

Remember the world number 97 had not won a Grand Slam match before this run.

And that's long... Novak Djokovic breaks back to level at 5-5.

Image source, AFP

What a response from the 21-year-old, popping a forehand right on the whites of the baseline and then picking out a pin-point winner.

He doesn't get the luck on another forehand that clips the net, though, dropping agonisingly on his own side.

Two break points Djokovic.

Chung clips the tape and Djokovic had to adjust quickly, sliding into a crosscourt forehand. The Korean can't eek his response high enough, rattling into the guts of the net.

Djokovic steals the next point, too - 0-30.

Now it's Hyeon Chung's turn to serve for the first set.

Youngest man left in the draw, bidding to become the first Korean to ever reach a Grand Slam quarter-final.

No pressure.

Novak Djokovic serving to stay in the first set, then.

He cruises to 30-0, follows up with a delicious ace that curls away from Hyeon Chung, who challenges... and gets it right, just wide, not so tasty after all.

That doesn't deter Djokovic. He rattles through to win the game to love.