Brutal shot from Federer down the line, but Tsitsipas counters with a big backhand of his own.

A "come on" from Federer as he gets on the board with his first serve.

The first point goes Stefanos Tsitsipas' way with a lovely, flowing cross-court backhand.

Image source, EPA

Russell Fuller
BBC tennis correspondent at Melbourne Park

You feel it's crucial for the underdog to strike first in a tie-break.

Tsitsipas doesn't half hit the ball hard.

He drop shots Federer who manages to get to the ball but flicks his low return into the net, but Federer nails his next few first serves to go 40-15 up.

Wallop. A service return goes long from Tsitsipas, and we're stopping at tie-break town.

Honestly. If you're going to seek out any shot from this match, make it that diving volley from Tsitsipas.

Here's Federer, serving to stay in the set.

A rare point on the Tsitsipas serve for Federer, as he floats a backhand into the net.

That's all Federer is going to get, though. Terrific serving from Tsitsipas, into the body, and he chucks a giant backhand beyond Federer!

That's a ridiculous shot. He hit it so hard he fell over!

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

It feels like the quality of the hitting has taken a boost over the last couple of games.

Federer wins the first two points on serve but that's a gorgeous backhand drive down the line from Tsitsipas.

Federer somehow keeps himself in a rally, spearing the ball fuller and fuller, before a mishit of a forehand just manages to land in!

40-15 to Federer, and the defending champion holds as Tsitsipas pushes a backhand long.

Tsitsipas hasn't dropped a point on serve in the past three games.

Over to you, Roger.

Tsitsipas hits the cover off a forehand down the line to muscle Federer out of a rally at 30-0.

Federer steps inside the baseline to meets Tsitsipas's serve but he skews his backhand long and the Greek holds again to love as a Federer punch takes a nibble off the net.

Federer is having to come forward more often, and he gets the advantage with a backhand winner.

A swinging first serve down the T from Federer, and Tsitsipas nets.

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

There are fairly even numbers in this match - five errors each but Tsitsipas has hit one more winner. Tsitsipas is matching the great maestro.

Image source, Getty Images

Up to the net comes Federer, meeting Tsitsipas's one-handed backhand with a volley of his own, and Tsitsipas can't angle a return around the net.

Hmm. Federer's forehand has gone a bit wonky as he twice sends the ball long, and then a passing swipe from Tsitsipas takes us to deuce!

What a strike that was. Tsitsipas opened up and let fly, somehow getting the ball to bounce just on the baseline.

These two met at the Hopman Cup earlier this year.

The match went the way of Federer after two tie-breaks.

Ooft. A sublime forehand from Stefanos Tsitsipas, right into the corner of the court, has Roger Federer stretching and he nets.

A big ace comes down for 40-0 and the Swiss, stranded behind the baseline, blazes his forehand into the foot of the net.

Federer unfurls a body serve to get the advantage.

And he holds as Tsitsipas spears a backhand long!

Image source, Getty Images

Federer gets himself to 40-15 before he's a passed by a belter of a forehand from Tsitsipas.

Now then. That's a big return from Tsitsipas and Federer, surprised, skews his own shot long.

Deuce.

Now Stefanos Tsitsipas is unhappy about a call on a Roger Federer serve.

It's called out, the umpire overruled and Tsitsipas, who had hammered his forehand into the net, eventually challenges after complaining about the overrule.

It's in. Everyone is very grouchy today.

A 128mph ace from Stefanos Tsitsipas gets his latest service game up and running.

A touch raggedy from Federer, spanking a backhand long, and Tsitsipas pops a terrific volley home to hold to love.

Image source, Reuters