Zing! Jan-Lennard Struff widens his shoulders and throws down a big forehand winner.

The pair exchange blows in a tough rally, and Federer slices into the net for 40-30.

But the Swiss second seed picks out a whipped forehand winner on the next point to hold.

Piers Newbery
BBC Sport at Melbourne Park

Federer and Struff begin almost unnoticed such is the hum of chatter, chinking of glasses, mass selfie-snapping and swaying to Dolly Parton. And that's just me. There is definitely a party atmosphere in here for this one.

I can report the temperature has plummeted to 33C as we approach 10pm local time, and it is now like sitting with a warm blanket clamped around your shoulders, rather than the hairdryer-in-the-face experience of this afternoon.

Der junge Deutsche will serve first in this second round match on the Rod Laver Arena.

The 6ft 5in 27-year-old has a massive serve and uses it with precision..

Struff moves to 40-15 when Federer goes long, but although he gets a little off balance on the next point, he sees out the game with a volley.

Nicely done.

What's in store for R-Fed today, then?

After beating former British representative Aljaz Bedene in the opening match of his title defence, Roger Federer now faces German Jan-Lennard Struff.

The world number 55 has never reached the third round of a Grand Slam before - he's got to the second round in all four majors.

The 27-year-old is looking to beat a top five player for only the second time in his career.

Struff has faced second seed Federer once before - on his home soil in Halle, Germany - when the Swiss won 6-4 7-6 (7-3).

Image source, Getty Images

It's been a fairly decent day for the men's seeds.

Novak Djokovic [14] beat Gael Monfils in four sets. Both players had to deal with rising temperatures of around 39C on court.

Fifth seed Dominic Thiem recovered from two sets down to beat American Denis Kudla, while Argentina's Juan Martin del Potro took four sets to see off Russian Karen Khachanov 6-4 7-6 (7-4) 6-7 (0-7) 6-4.

Fourth seed Alexander Zverev beat fellow German Peter Gojowczyk 6-1 6-3 4-6 6-3.

But it's all over for American Sam Querrey and Belgium's David Goffin.

Querrey, the 13th seed, was beaten by world number 80 Marton Fucsovics while Goffin lost to 36-year-old Julien Benneteau.

And it's not going so well for former champion Stan Wawrinka, who's a set and 4-0 down against Tennys Sandgren.

Image source, Getty Images

Piers Newbery
BBC Sport at Melbourne Park

You have to move pretty fast around here if there's a whiff of free cake, especially when donated by Angelique Kerber on her 30th birthday. Maybe next year...

Image source, BBC Sport

Kerber celebrated her birthday with a win over Donna Vekic earlier today.

Next up is Maria Sharapova.

In the women's draw...

British number one and ninth seed Johanna Konta suffered a shock defeat by world number 123 Bernarda Pera in the second round of the Australian Open.

The American won 6-4 7-5 to claim only her second win at Grand Slam level.

World number one Simona Halep cruised past Eugenie Bouchard of Canada 6-2 6-2, but Garbine Muguruza - the Wimbledon champion - lost 7-6 (7-1) 6-4) against world number 88 Hsieh Su-Wei.

American Madison Keys took only 41 minutes to beat Ekaterina Alexandrova of Russia.

Five-time Grand Slam champion Maria Sharapova beat 14th seed Anastasija Sevastova in straight sets.

For a full list of results and reaction, head to our dedicated tennis page.

Image source, Getty Images

Hi, we're back!

It's almost time for a bit of Federer, but let's first catch up on what's happened on day four in Melbourne.

We're going to take a short typing break so we can limber up for Federer v Struff, who are due on Rod Laver Arena after the conclusion of Ashleigh Barty's match with Camila Giorgi.

It looks like that one could go the distance.

Keep up with the live scores here and stay on this page to hear BBC Radio 5 live sports extra's coverage.

Brb.

Piers Newbery
BBC Sport at Melbourne Park

It might be cooling down, slightly, as the evening unfolds but the talk here remains about the heat, and whether or not it reached dangerous levels today. Especially with the temperature expected to rise on Friday.

“Good luck for the guys," said a rueful Gael Monfils after his brutal loss to Novak Djokovic in the afternoon heat.

“I’m telling you I was dying on the court for 40 minutes. Sometimes we put our bodies at risk so just be smart and, if you have to give up, it’s not a shame.”

Djokovic himself said it was "one of the toughest" matches he has played, adding: “Today it was right at the limit.”

Simona Halep speaking on court after her win: "I think I played well. I felt the ball well. It's always tough as she hits the ball so fast. I knew I had to open up the court and I did it well.

"I'm happy to play in the third round again. I just want to enjoy my time here, even though I'm a bit injured."

Halep turned her ankle in her first round win over Destanee Aiava, and she said of her injury: "I feel pain but I didn't think about it. I just wanted to play the match."

She's asked about being world number one and her Australian coach, Darren Cahill.

"I don't feel pressure," said the 26-year-old. "I just enjoy the moment. I expect tough matches.

"I can say I'm a little bit Australian as well because of Darren. I've worked with him for six years, and I've reached number one with him."

A superb backhand winner sends Halep on her way, but Bouchard responds on the forehand.

And then the Romanian sends a forehand miles over the line for 30-30, and then over the baseline.

Break point Bouchard! Oh, it's saved. Deuce.

Halep brings up the advantage for match point...

Image source, Reuters

A double fault is not what Eugenie Bouchard needs in this situation.

But thanks to a slap into the net from her Romanian opponent, the world number 112 levels at 30-30.

Then she hits long, offering Halep another break point, and Bouchard lets out a big sigh.

The Canadian gets her concentration back, and after a pinging rally, she backhand volleys over for deuce.

But, a few seconds later, Halep brings up another break point. The world number one scoops her body down low to outsmart Bouchard and she's a game away from the win.

Simona Halep is looking very, very comfortable. A hold to 15 follows in the next game and she's edging closer to the third round.

After 50 minutes, Australian Ashleigh Barty has lost the first set 7-5 against Camila Giorgi.

It looks like we might be waiting a while to see Roger Federer on Rod Laver Arena, seeing as he's due on after Barty's match is finished.

Eugenie Bouchard's head is hanging low as she's overpowered by the world number one.

Two more break points to Halep.

Bouchard slaps the net with a bit of a careless-looking forehand. Halep's on the charge again.

Cake? Who said cake? I'm on my way.

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Halep holds with relative ease. The service games have settled somewhat after six breaks in the first set.

They say life begins at 30, unless you've already won the Australian Open and US Open, that is...

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