Leon Smith
GB Davis Cup captain on BBC Radio 5 live sports extra

"It's a long time since I've seen Roger as agitated as that. But it's important that Wawrinka keeps his nerve and builds on the break of serve."

All good matches need some controversy. Federer is unhappy at an over-rule by the umpire at the start of the third set. It seems to throw Federer off his stride as well, as Wawrinka break.

The first point of the set went in favour of Wawrinka, whose cross court shot was called out by the line judge. The umpire immediately over-ruled and called 0-15. Federer did not hear that and only realised when he lined up to serve at 0-40 that the first point had gone against him.

He argued with the umpire that he would have challenged his over-rule had he heard. TV replays show Federer would have been right to challenge.

Leon Smith
GB Davis Cup captain on BBC Radio 5 live sports extra

"You just sensed towards the end of that set that Federer was holding on his own serve quite easily and there was not a lot of time for Wawrinka between his service games.

"It's what we wanted though, a third set. Or a one-set shoot-out to see who plays Novak Djokovic on Sunday."

30-0 to Federer on Wawrinka's serve. The server then smashes an overhead attempt into the net to give Federer three set points.

Image source, Getty Images

An attempted cross-court backhand only hits the top of the net from Wawrinka and it is one set each. And what a match. A contender for the best of the tournament so far.

But Federer doesn't let anything slip through his fingers. His service game is fine, and takes us to 6-5. Once again Wawrinka is serving to save the second set.

A poor sign for Tottenham fans. BBC Radio 5 live sports extra commentator Leon Smith reports that a stray shot heads in the direction of reserve Spurs goalkeeper Brad Friedel.

Image source, AFP

The American is among the O2 crowd, but spills a catch that heads his way off Wawrinka's racquet.

Some more stats for you. Wawrinka has only got 40% of his first serves in play, but has then lost only two points when doing so. He also leads the aces count, by 7-3. He holds his serve in the 10th game as the prospect of a tie-break gets closer.

That is 10 consecutive holds of serve in this set.

Leon Smith
GB Davis Cup captain on BBC Radio 5 live sports extra

"Roger needed a straightforward service game. He can now apply a lot of pressure on Wawrinka's service game. Wawrinka knows he will have a lot of pressure on him. His first serve percentage is still poor and he's been relying on slightly sloppy return of serves from Roger. I'm pretty sure he won't get that from Roger in this next game."

Back to matters in London. Wawrinka at 40-0 down, wins his first point of the game with his fifth backhand winner of the match, but that doesn't phase Federer, who takes the next point.

Wawrinka is now serving to stay in the set.

More from our earlier question and answer Facebook session, external with former British number one Tim Henman.

Jonathan Dixon: "Looking ahead to next season can you see Nadal winning the French Open for a 10th time or will his injury problems mean someone else will be favourite even though clay is Nadal's best surface?"

Image source, AFP

TH: "I still think Nadal goes in as the slight favourite when he's won nine times before - it's an incredible achievement and it's a surface that I think he's more dominant on than any other player in history.

"But with Djokovic having never won the French, that is going to be a huge motivating factor. Those are the two players to beat."

Russell Fuller
BBC tennis correspondent on Radio 5 live sports extra

"The longer this goes on, the less margin of error for Federer. One poor service game and his season could be over."

Who is going to blink first in this set? At 30-30 on Wawrinka's serve, the door is slightly ajar for Federer to take advantage.

But as soon as the opportunity comes, it looks to have gone. But wait. It is deuce - for the third game in a row.

Another one for you stat fans. Unforced errors so far in the match. Wawrinka 21, Federer 14. But Stan's serving is getting him out of trouble and eventually helps him hold his serve. He leads overall, and it is 4-4 in a very tense second set.

A full-stretch Federer just manages to get his racquet on Wawrinka's attempted pass. The world number two is pumped up, and screams out while punching the air.

If both players play like this next week then Switzerland will take some stopping in the Davis Cup final against France. A 23-shot rally, while at deuce, gets a great reaction from an enthralled crowd. Before Federer holds again after an aggressive second serve of 106mph down the T.

Image source, Getty Images

Some serving stats for you. Wawrinka's average first serve speed is coming in at 129mph, compared to 118mph from Federer.

Leon Smith
GB Davis Cup captain on BBC Radio 5 live sports extra

"He had two massive serves to get him out of trouble in that game. It's amazing his serve percentage is so low at around 40% because it seems like he's serving well. But when he gets his first serve in, he wins just about every point."

Wawrinka has won all but one point when he has got his first serve in.

Federer goes into defensive mode, and it's like hitting against a brick wall. Everything Wawrinka throws at him, Federer returns. It is 0-30 on Wawrinka's serve, but another ace, his fifth of the match so far, gives him some momentum to fightback.

Federer wastes two break points, but, after going to deuce, has another chance, which Wawrinka again saves, before holding. And it is a great hold from 0-30 and 15-40 down.

We said we hoped it would be a high-quality encounter. It certainly is. Novak Djokovic said he would be watching and he must be enjoying both players tiring the other one out. I wonder if the Serb remembered the popcorn.

Leon Smith
GB Davis Cup captain on BBC Radio 5 live sports extra

Image source, AFP

"We are certainly seeing more net plays from Federer. It's something we'll see continue as this match goes on. And maybe he'll try to pull Stan into the net and test his skills and movement in that area of the court."

Some straight-forward serve-volley tactics from Federer are seen in the fifth game of the second set. He has decided to charge into the net, just to give Wawrinka something to think about.

Under pressure from a hovering Federer, Wawrinka slaps a backhand into the top of the net. It is tight and tense, with both players trying to out-think and out-battle their opponents. But it is making for a compelling encounter.

An important, if unspectacular, hold from Wawrinka. He won't be telling his grandchildren about it while sitting in a rocking chair in 50 years time, but it is enough to do the job. 2-2 in the second.

Another of Tim Henman's answers from our Facebook question and answer session.

Image source, Getty Images

Emmacy De Paragon: Do you think Roger Federer can reclaim world number one?

TH: It's very difficult for him with Djokovic's consistency right now. I think he's the player to beat. I think Roger can win a Grand Slam again but over a 12-month period to be number one is going to be very difficult.