Anyway, back to the action.

Mark Williams is well settled and is building a break in this 25th frame. His calmness and experience will be so useful in tonight's session.

A clever cannon onto the black to set it up after a tricky red ensures he will stay at the table for now.

A little behind-the-scenes note on the players chatting back stage before being introduced to the crowd - at BBC Towers we get the raw TV feed with the natural sounds from the Crucible. When Williams and Trump were chatting backstage before this match, there was someone noisily vacuuming in the background.

Kind of removes the glamour of the whole affair.

Another loose shot by Trump, and this time Williams finds his mark with the long pot.

Not a great start by world number one Trump - falling three frames behind in such a tightly contested match will be difficult to come back from.

Judd Trump breaks us off in the 25th frame, and the first of the evening.

It's not a great break, leaving Mark Williams with the chance of a long pot into the bottom left - but the Welshman's radar is not quite calibrated yet.

Here come the players, to incredible ovations from the Crucible crowd.

It sounds like it will be a superb atmosphere in Sheffield tonight.

Image source, BBC Sport

Mark Williams just about sneaks on to this graph of the most successful players in Crucible history with three world titles.

A fourth would see him draw level with Mark Selby and John Higgins, but he has to get past world number one Judd Trump yet, and that will be no easy feat.

A reminder that, not too long ago, these players met in the Crucible semi-finals - and it went all the way down to the wire.

In 2022, Judd Trump beat Mark Williams 17-16. On that occasion, Williams came from 7-1 and 11-5 down to lead 16-15, only for Trump to win the last two frames and seal one of the most remarkable victories in Championship history.

If we have another final frame decider today, no-one will be complaining.

Steve Sutcliffe
BBC Sport at the Crucible Theatre, Sheffield

Whoever wins this evening can expect to have to do multiple media interviews afterwards and they are then likely to be greeted by a healthy posse of fans at the stage door entrance like Zhao Xintong on Friday evening.

I can't see anyone getting away too early, put it that way.

BBC Two

Live coverage of today's World Championship semi-final is available right now on BBC Two. You can also watch via BBC iPlayer.

Alternatively you can follow the action by clicking on the 'Watch and listen' tab above.

Shaun Murphy
2005 world champion on BBC Two

If Judd Trump gets among the balls he's not the player he was a few years ago where he gets first chance high on the blue, or low on the black, and then smashes the reds everywhere. He's much more considered. It's all about keeping the balls together should the break fall apart. Not many players do that.

John Parrott
1991 world champion on BBC Two

Mark Williams is 50 years of age. To be producing what he is producing is just off the charts. He has got the world number one on the ropes here.

If that morning session would have carried on Mark would have been the winner because he is in the ascendency. Judd Trump has to find something. I'm not sure what it is because Mark is playing so well.

Steve Sutcliffe
BBC Sport at the Crucible Theatre, Sheffield

This mouth-watering contest between the two most decorated players in snooker is the only place to be tonight in Sheffield.

Large queues were already forming at 17:40 BST.

A reminder that the World Championship semi-final matches are best of 33 frames.

So it's first to 17 wins and we will play to a finish this evening.

John Parrott
1991 world champion on BBC Two

Mark Williams was potting the reds right in the middle of the pockets in the morning session - they are not touching the jaw.

Yesterday, Mark went two frames behind and fought back and Judd Trump has do the same. The world number one is under the cosh heading into the evening session.

Shaun Murphy
2005 world champion on BBC Two

Mark Williams' potting has just been outrageous. We used to say he's the best single-ball potter in the world 25 years ago and he's probably still that! When you collide that with an incredible amount of old school nous.

Steve Sutcliffe
BBC Sport at the Crucible Theatre, Sheffield

Image source, Getty Images

Three-time champion Mark Williams takes a 13-11 lead over Judd Trump into the concluding session of their World Championship semi-final on Saturday evening.

An absorbing morning of play started with the players level at 8-8 after Williams recovered from 7-3 down to rein in the world number one on Friday in Sheffield.

Williams, 50, who is bidding to become the oldest Crucible finalist, continued in the same vein, crafting four half-centuries as he took five of the eight frames on offer.

He opened up with a break of 57 and, while Trump responded with consecutive runs of 71 to edge back ahead, the Welshman then reeled off the next three frames.

Englishman Trump, who has won 30 ranking events in his career and reached six finals this season, constructed a timely 64 to reduce his arrears to 12-11.

However, Williams, whom Trump defeated 17-16 in their thrilling last-four meeting in 2022, composed a 62 in the 24th frame of their best-of-33 encounter to give himself a two-frame cushion.

Read the full report...

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This could be a late one...

Welcome back to the Crucible, where Mark Williams and Judd Trump will play to a finish in this session to decide who earns a place alongside Zhao Xintong in this year's final.

You could hardly fit a cigarette paper between the two men across the first three sessions of this match. Will we go to a final frame decider? Let's find out.

We are going to pause our live text commentary for the moment but will be back with you for the climax of Mark Williams vs Judd Trump at 18:45 BST this evening.

A reminder that coverage will start on BBC Two at 19:00.

Make sure you read Steve Sutcliffe's report from this morning's session at the Crucible..

Here's some other snooker stories to read between now and tonight which might tickle your fancy:

• O'Sullivan to leave UK to live in Middle East
• Williams has 'big decision' to make on eye surgery
• Is snooker 'dying' in Scotland? Or is it just 'different'?
• 'National hero' - China's pursuit of an elusive world title