Serve and volley from Federer...

And Tsitsipas blasts his backhand into the net!

Russell Fuller
BBC tennis correspondent at Melbourne Park

We are seeing some uncharacteristic errors from Federer.

This is not Federer in total command of his game because he's being pressurised by Tsitsipas.

Federer challenges a Tsitsipas ace.

This looks in... and it is!

Set point to Tsitsipas.

WHAT a set this is.

Federer has a chance, popping his returns deep, but he's too eager to pull the trigger on a big forehand.

10 (TEN) all.

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

It's been neck and neck from the opening point. They've been so evenly matched in this set.

Image source, EPA

Big first serve from Federer, followed by the dinkiest of drop shots.

He's got himself another set point.

... My hands hurt.

Nice.

Forward comes Federer and smashes his way back to parity.

Federer thinks he's got Tsitsipas off-balance with a swipe cross-court.

He hasn't, though - great return from Tsitsipas and Federer misses a straightforward forehand.

Set point for Tsitsipas.

Image source, EPA

Block return from Federer... and it's drifted long!

And now, Federer goes down the T, and Tsitsipas' backhand return goes long!

Another set point for Federer.

Wallop.

Big first serve from Federer. Set point saved.

Terrific all-court tennis - and it's Federer who blinks first!

That's a wayward forehand and now it's Tsitsipas with set point.

OH!

What a way to save set point! Tsitsipas leaves Federer sprawling with a huge strike cross-court, and then he darts forward to volley the winner.

Image source, Getty Images

Federer's forehand goes temporarily missing, and Tsitsipas draws level.

Terrific body serve, and it's set point, Federer.

Stefanos Tsitsipas has rightly spoken to the umpire, who asks the crowd not to make noise while the players are in a rally.

There seemed to be a yell when Federer hit a particularly deep return.

Gorgeous from Tsitsipas, pumping a forehand into the corner of the court.

And then Federer rips a furious forehand down the line that the Greek can't return!

Jonathan Jurejko
BBC Sport at Melbourne Park

Back inside Laver... and, as expected, there are not so many Greek fans. Those backing Tsitsipas are being drowned out by Fed Heads.

"Let's go Roger, let's go!" gets an airing at that changeover.

Image source, AFP

Serve and volley from Federer, and Tsitsipas' lob drifts just long.

Time for a change of ends, and Federer pumps a big first serve down the T to take the lead.

A bit too much oomph on that backhand from Tsitsipas, but he restores his lead with an ace.