Selby leads 20-11 in the 13th frame. But the balls are not positioned well so it may well be a long frame.

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Boxer Paul Smith Junior,, external the British super-middleweight champion, is used to going toe-to-toe with opponents and is enjoying the Crucible tussle.

He tweeted: "Watching the gas-cooker on BBC2. Mr @ronnieo147 is the best player to ever pick up a cue. Unbelievable. #Snooker #snookerworldchampionship"

Former world champion Ken Doherty says: "Playing late last night may have affected Mark today, but the adrenalin normally kicks in.

"It is really important to try and limit the damage in tonight's session and then come back tomorrow and play better. He needs to get a good night's sleep, but when you are in a final it is very difficult.

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"When I was in the finals here I would have been happy if I got three or four hours sleep. I always had that nervous energy when I was in a final and I would try and visualise winning the trophy and I would lie awake just thinking about that."

During the interval, BBC Two ran a pre-recorded interview with Mark Selby. He said: "I think mental toughness is one of my biggest weapons, but I have shown in the past I can win on my B game.

"My childhood dream was to become a world champion and it will mean everything.

"The standard is so tough. It's so hard to win, you know you will have bad sessions, it's just how bad a session you will have."

Once again, we have a re-rack. Selby smashes in a long red when we get started again. He spent the interval on the practice table and has instantly produced one of his best shots of the match at the start of the 13th frame.

Former world champion Ken Doherty has been speaking to us during the interval and says: "Players do different things during the mid-session intervals.

"If you are happy with how things are going, you sit in the dressing room, have a cup of tea, talk to your confidante, who will give you a bit of a boost.

"If you aren't playing well, like Mark Selby, you head to the practice table and you just hope to pot a few balls and get your confidence going again. At the moment his arm looks like it is very tense."

We are back under way at the Crucible. We have five frames left today. If Selby wins them all then he would have an overnight lead. What a story that would be. We will see what happens.

At the mid-session interval, Ronnie O'Sullivan has claimed 761 points in comparison to Mark Selby's 477 points. O'Sullivan also has the superior pot ratio (90% v 86%), while Selby's safety success (78% v 73%) is actually superior.

For those who complain about Selby's pace of play, they may be interested to know he averages 26 seconds a shot, while O'Sullivan averages 21 seconds a shot.

More from O'Sullivan: "When I first started working with [psychiatrist] Steve Peters we set dream goals. And one of mine was to win a world title in my forties. I'm 39 this year and everyone else who is doing well is 30 or 31.

"I feel blessed to be mixing it with this era of snooker players. It makes you feel young.

"I'm happy to come now and if I lose I won't beat myself up. It's about me going to work, doing what I do and living the dream."

Ronnie O'Sullivan on BBC TV prior to today's final: "When you play well you don't panic. But it's when you are not playing well, that's when the panic sets in.

"But you can't play well every day and you need to accept that. Mark will always give you problems as he has a great tactical game. I've learned to admire Mark more now.

"I have to pinch myself that I'm in the final again. I'm content with five [world titles] but who would not want to be a world record holder?"

Stephen Hendry
Seven-time world champion on BBC TV

"I still get angry when I play exhibitions so I will have to see."

Steve Davis
Six-time world champion on BBC TV

"It's a great fun idea so we will have to see how many players take up the offer."

John Parrott
Former world champion on BBC TV

"While there are golf courses in the world I won't be getting out my cue. I'm getting my clubs out."

World Snooker chairman Barry Hearn on plans to extend the tournament: "We want to increase the number of players and will invite any player who has won the World Snooker Championship in the past and also from emerging nations."

The 1997 world champion Ken Doherty is going to be joining us online and pitching in with some observations in the first frame after the interval.

Do you have a question for Ken? Sends us a message on Twitter, using the hashtag #bbcsnooker.

Some more of your comments, using #bbcsnooker on Twitter.

James Stevenson:, external I think Selby needs to win three of the five frames left tonight to stand any chance tomorrow.

Alex Ian:, external Ronnie might not be the best player of all time, but he's certainly the most intimidating player of all time.

Ally Atherton:, external Hendry and Davis were excellent too. But Ronnie is the most entertaining to watch as well as being fantastic.

John Parrott
Former world champion on BBC TV

"We can all play when it is easy, but it is when you are under a cloud that's when it matters. So, well done to Mark, who is obviously not feeling great."

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The second session has mirrored the first one. O'Sullivan has won the opening three frames of both sessions, before Selby has claimed the frame just before the mid-session interval.

Ronnie O'Sullivan 8-4 Mark Selby (25-82, Selby 55 break)

Mark Selby's break of 55 is his highest of the match. That statistic is nothing to shout about, but it is a start.

He should wrap up the frame with a thin cut on the pink. It is unsuccessful though and hovers tantalisingly over the pocket. That would have given him his first frame of the evening session.

Instead, there is a shake of the head and a wonder of what might have been. O'Sullivan needs one snooker, but Selby should have finished this frame already.

George Riley
BBC Radio 5 live at the Crucible

"I've looked at the last 10 World finals and seven have been won by the player who finished his semi-final first and had more rest."