Jannik Sinner is pulled wide and nets a forehand. Break point saved. Deuce.

Djokovic pulls a point back with a strong serve but then sends down a tame volley to set up a backhand pass into acres of space for Jannik Sinner.

Is this the moment? Novak Djokovic starts the game with an ace but is quickly his own worst enemy, sending a forehand long for 15-30.

Russell Fuller
BBC tennis correspondent on BBC Radio 5 Sports Extra

All of the statistics make it look as if Sinner should have won this match by now.

51 winners to 29 unforced errors which is a fantastic margain.

Yet, he is very well in danger of being dragged into a fifth set.

Annabel Croft
Former British number one on BBC Radio 5 Sports Extra

That is 19 aces for Sinner now - absolutely incredible.

And I thought Djokovic was going well with eight!

Hmmmm. Jannik Sinner is looking good at 40-15, including another two aces, but then he floats a backhand long to invite a bit of a pressure on himself.

He comes through it, producing a big first serve to Novak Djokovic's backhand.

Another hold ticked off but what he really needs is a break point.

Image source, Reuters

Novak Djokovic chastises himself for missing a backhand and responds with an ace.

He then uses his forehand to manoeuvre himself into a winning position. Back-to-back inside out strokes force Jannik Sinner off the court and he drags the Italian to the opposite corner before firing down a winner with a roar.

There's time for another ace before he completes the hold to 15.

Image source, Reuters

What a time to find a few big first serves. An ace down the T and one which makes the familiar clattering sound of ball on frame.

Jannik Sinner holds to 15.

Annabel Croft
Former British number one on BBC Radio 5 Sports Extra

There is a lot of stretches down the end of Novak Djokovic. A lot of yoga poses and hip flexor looseners.

He is starting to feel it I think, two hours 38 minutes on the clock.

Jannik Sinner enjoys a rare moment on top in a baseline exchange thanks to a deep return. Novak Djokovic comes up with a forehand error but wins the next two points to hold to 15.

The clock has just ticked past midnight in Melbourne. Djokovic does some stretches.

Russell Fuller
BBC tennis correspondent on BBC Radio 5 Sports Extra

No man in the open era has reached an Australian Open final older than Djokovic is now.

Ken Rosewall was 37 when he reached the final in 1972. Djokovic is 38, turning 39 in May.

It would be some story, and there is still hope for Djokovic

Novak Djokovic can only raise his thumb in appreciation as Jannik Sinner opts for an audacious top-spin lob and lands it just inside the baseline.

With a fairly swift hold to 15, the Italian is up and running in the fourth set.

Pat Cash
Former Wimbledon champion on BBC Radio 5 Sports Extra

There is a lot of unforced errors coming from Sinner. I don't think he has timed the ball particularly well at all today.

There is too many short shots to allow Djokovic to pull the trigger on the forehand.

Image source, Getty Images

From 30-0 up, Novak Djokovic can only recoil in disgust as he misses the line with a forehand to offer Jannik Sinner a route back in the game.

He rediscovers his equilibrium to hold to 15, nailing yet another down the line forehand winner.

Jannik Sinner thought about coming in, dillied, dallied, was forced into a retreat and surrendered the game with a loose forehand.

Strap in.

Another backhand error from Jannik Sinner, this one going long in reply to a deep forehand from Novak Djokovic.

Jannik Sinner saves the break point with a forehand drive volley, following a serve into the net.

Jannik Sinner pulls a backhand into the tramlines.

Jannik Sinner opens the fourth set with an ace. It's one of three in the game, alternating with forehand winners for Novak Djokovic. Deuce.

Image source, EPA

That wasn't far away! Jannik Sinner whips a cross-court forehand on the run but it's about an inch out.

No matter - he secures the break and the third set at the second attempt, Novak Djokovic sending a lob long.