Marin Cilic has only been broken three times in this entire tournament. Could number four be on the cards?

He swipes a backhand wide and Federer has two break points in the bag.

The Croat saves one with a lovely drop shot, and then a forehand error takes us to deuce.

Cilic eventually holds after Federer hits into the net.

Jeff Tarango
Former professional tennis player on BBC Radio 5 live

Cilic has been so dominant in this tournament and 90% of first serve points he has won - that is incredible.

People wonder about his shot variety, but when you come to grass you can just play your biggest shot all of the time.

Roger has to have a good serving day to keep Cilic on the back foot.

Image source, AP

The Centre Court crowd let out a groan as Roger Federer swipes a forehand into the net for 40-30.

But then they're back to cheering the world number three as he whacks an ace down court to hold. 

All the emotions here in SW19.

Image source, Reuters

Peter Fleming
Seven-time Grand Slam doubles champion

When Querrey played Djokovic, he knew he had to red-line it. There was no question about the tactics he had to employ. Here against Raonic, he might be tempted to play a consistent game from the back.

Image source, EPA

Sam Harvey-O'Connell: Unpatriotic of me but I want Federer to win one more slam. Best there ever has been   

John McEnerney:  Both Murray & Fed should get the full shot workouts they badly need, MC & Jo Wil are no slouches both 4 setters!  

James Pegram: Federer in 4 sets and Murray in 4 sets to progress at #Wimbledon, external today.  

Jonathan Jurejko
BBC Sport at Wimbledon

Quite a few empty seats dotted around Court One - ticket holders are obviously banking on this one going long into the sunny SW19 afternoon. 

It's a battle of the monster serves and the tone is set with Raonic's first thunderous effort. The line judge has to hastily duck out of the way as the ball thumps into the cover behind. That raises a few worried laughs. 

Tim Henman
Former British number one on BBC TV

The start is important for Cilic. Federer is such a good front runner that Cilic needs to get off to a good start.

Jim Courier
Former world number one on BBC TV

When Cilic makes his first serve he is winning 90 per cent of points. 

This is a man who came into Wimbledon with a sub par season serving-wise. He has captured form right at the right time. 

Image source, BBC Sport

When you're 5ft 3ins like I am (Caroline on the keys, by the way), everyone seems tall.

But Marin Cilic is huge. Bloomin' huge. And the 6ft 6ins Croat has a hefty serve to match.

He holds to love in the opening game against Federer on Centre Court.

But Federer is unnerved. Cool as you like, the Swiss also takes all four points on his service game. 

Bosh.

Image source, EPA

They're also out on Court One. 

You can watch Milos Raonic v Djokovic-beating Sam Querrey on this link. 

It was a simple straight sets win for Martina Navratilova and Selima Sfar against Anne Keothavong and Melanie South 6-1 6-3. 

During the match former British number one, Keothavong, was having problems serving... much to Navratilova, and the crowd's, amusement. 

Jim Courier
Former world number one on BBC TV

This is a tricky match up for Federer. Cilic can take the game out of his hands.

He has a monster serve and if given time on the ball he could present a lot of trouble for Roger Federer.

Down on court 12 we've had our first retirement of the day.  Medina Garrigues and Parra Santonja were trailing 5-3 in the first set before Garrigues became injured.

But in the final point, she managed to smack her partner on the back with the ball. Game, set, ouch! 

Jonathan Jurejko
BBC Sport at Wimbledon

Image source, BBC Sport

These 'Fed Heads' have some remarkable stories. Not only are Sarah Cassidy-Seyoum (she's on the left) and Myriam Khalin (that's her on the right) kitted out in eye-catching headwear, t-shirts and scarves, they also have a colourful tale to tell.

Sarah has travelled over from Connecticut in the United States, while Myriam has arrived at Wimbledon from Lebanese capital Beirut. How did they meet? In the queue last year. So they kept in touch over social media and arranged to meet up again this year.

They will be on Centre shortly to watch their man and, of course, reckon he'll be triumphant.

"Yes he will in three sets today," Sarah boldly predicts. "Will he win the whole thing? Of course. I said he would win in 2012 and I'm saying it again."

'Woop, woop, woop' go the Centre Court crowd as Roger Federer and Marin Cilic walk out onto the grass.

It is officially roasting out there. Why Federer's got a jacket on, I'll never know. 

British pair Anna Smith and Neal Skupski beat the number one seeds yesterday and today face 14th seeds Aisam Qureshi and Yaroslava Shvedova. The latter was a quarter-finalist yesterday in the women's singles.

Caroline Chapman
BBC Sport at Wimbledon

This is the serve that will face Andy Murray later on this afternoon. It's pretty brutal.

Jo-Wilfried Tsonga is out on the practice courts, having a knock about with Lucas Pouille, who will play his quarter final against Tomas Berdych on Court One later.

Image source, BBC Sport

I always thought my favourite mash-up was when Freelance Hellraiser blended the Strokes, external into three-and-a-half minutes of bootleg magnificence.

But then I saw BBC Sport's sublime summation of Open era Wimbledon champions.

Feast your eyes on this. And stick on a bit of Freelance Hellraiser to soundtrack it., external