Kyrgios is teetering. Both in this game and in terms of temperament.

Grigor Dimitrov slices a forehand winner to earn another break point - and there's another outpouring of expletives from the Australian.

Nightmare! Kyrgios, off perhaps the easiest point of the match, slams a volley from midcourt into the net. Dimitrov breaks.

Leon Smith
GB Davis Cup captain on BBC Radio 5 live sports extra

That was the most conservative serve Kyrgios has hit this match but all credit to Dimitrov because he went on the offensive and got in charge of the rally to create break point.

But then Kyrgios hits his 34th ace and it's back to square one for Dimitrov who just walked over to the other side of the court to face the next one.

Magnificent from Grigor Dimitrov.

He fires a forehand across court with more spin than a general election and Nick Kyrgios can't deal with it.

Break point.... saved, with another huge ace.

An ace to follow a double fault? No problem for Nick Kyrgios.

Grigor Dimitrov challenges, but that's kissed the line.

The Australian goes long with his next shot, though, and there's a few choice words to follow.

Brilliant from Nick Kyrgios, working his opponent around the court before lunging forward to take the volley on his backhand side and slicing it into the space vacated by Grigor Dimitrov.

He follows up with a double fault - and then blames someone in the crowd for coughing.

Deuce.

We've reached the three-hour mark. Three enthralling hours it must be said.

Nick Kyrgios hammers in his 31st ace of the match, but can then only top a straightforward forehand into the roots of the net.

Dimitrov challenges what could be another ace. But it's in. Postage stamp stuff.

Neat from Grigor Dimitrov.

Pushing Nick Kyrgios left, and then right before darting to the net to hammer a volley home.

Dimitrov cruises to 40-0, and the Australian then goes long.

Dimitrov has his head in his hands again, this time after a loose forehand that drifts wide.

Kyrgios attacks with a punishing forehand of his own and Dimitrov can only stick his response in the tramlines.

An ace to finish. That's 3-3.

Leon Smith
GB Davis Cup captain on BBC Radio 5 live sports extra

This is a great match. Everyone was looking forward to it and it's living up to expectations.

Image source, AFP

That's a massive second serve from Nick Kyrgios.

Grigor Dimitrov shakes his head in frustration. Or disbelief?

David Law
Radio 5 live sports extra commentator at Melbourne Park

Everyone is catching their breath and taking the chance to stretch their legs because there could be another two hours of this classic.

Big serve at a big time for Grigor Dimitrov. He needed that.

Another follows, rattling the racquet of Nick Kyrgios and dropping to the blue floor in front of him.

Wonderful from the third seed. A superbly taken forehand winner to turn this game back in his favour.

Nick Kyrgios whacks the top of the net with a thunderous forehand, but it trickles agonisingly down on to his own side.

Grigor Dimitrov miscues and that's deuce, before Kyrgios hits a running forehand with outrageous speed to earn a break point chance.

Well, it's like musical chairs in the Kyrgios box at the minute - up, down, jostling around.

More importantly, on the court, it's Dimitrov who coaxes a smart forehand winner beyond the Australian, only to watch his attempt at a slapping forehand pass catch the frame.

Unbelievable, I think Kyrgios has just been screaming at his box to stand up?

They obey... but he pops a sloppy backhand long with a straight racquet and we're at deuce again.

Two big points, two ferocious strokes as the 17th seed takes a huge hold.

Image source, EPA

We're back at deuce.

The Australian looked to be in control of the rally, but he slips a forehand long.

Dimitrov's hands reverberate from the speed of the Kyrgios serve, and the ball flops off his strings into the net.

But that's a third deuce. Kyrgios just can't close this one out.

Kyrgios whacks a ball into the crowd, and it's a great catch from one spectator!

He then saves one break point by slamming down an ace, before nailing his 28th of the match to bring it back to deuce.

Dimitrov loops a loose backhand slice wide. "Let's go," screams Kyrgios.

Double fault from Nick Kyrgios.

Two break points Grigor Dimitrov.

If you missed it earlier, Kyle Edmund awaits the winner of this one in the quarter-finals...

It's like one big party at Rod Laver Arena at the minute, music blaring out between points. How do you find your concentration amid that?

Kyrgios goes long, while Dimitrov looks completely unfazed. He has to scramble back around a Kyrgios shot that was going one way, hits the net, and drifts the other.

But Dimitrov works the return and the Australian is off target - 15-30.

We're whistling through the first few services games of the fourth set.

Power upon power, ferocious serve upon ferocious serve - that ball has taken some battering.

Dimitrov takes it.