After a break of 39 a tricky cut on the black into the corner pocket stymies Mark Williams and Judd Trump gets his chance with the balls evenly spread. Can he capitalise?

Mark Williams with a promising early break, including a plant into the middle pocket. He's opened up the pack nicely and working the black.

The Welshman looks to have a bit of momentum here.

We are back from the mid-session interval suitably refreshed.

Judd Trump to break.

Stephen Hendry
Seven-time world champion on BBC Two

The standard of snooker Mark Williams has played in these last two frames has been wonderful. It's the semi-final of the World Championship and you would expect that. His response to missing that black on the spot a few ago, we spoke about his temperament but it's phenomenal.

BBC Radio 3 Unwind's Niall Breslin looks at how the intense pressure at the Crucible can affect a snooker player's mental health and the importance of mental skills for all sportspeople.

Available to UK users only.

Steve Sutcliffe
BBC Sport at the Crucible Theatre, Sheffield

Mark Williams' coach Lee Walker was doing shuttles down the back corridor towards the back end of those first four frames.

Williams called Walker the self-proclaimed best coach in the world the other day after advancing past John Higgins 13-12 in an absolute thriller.

Whatever he did manage to say to Williams certainly did the trick there.

Steve Davis
Six-time world champion on BBC Two

Mark Williams is one of the most talented players we've seen in the game. He might not be as demonstrative as some - he's not crash, bang, wallop - but he has a level of skill very few people have got.

Dennis Taylor
1985 world champion on BBC Two

An absolutely incredible finish before the mid-session interval! This Crucible crowd have enjoyed this entertainment.

Haha, not quite the century but some great entertainment as Williams plays a spectacular attempted trick shot - then draws laughs from the crowd as he uses his hand to try and block the brown from going in-off.

It's a two-frame gap between the players at the mid-session interval.

After Judd Trump dominated the first frame this afternoon, Mark Williams has come back with some excellent snooker.

A silly error handed the second frame to Trump, but Williams has handily won the final two and he is certainly in this semi.

Right now, Williams is building towards what would be the 100th century break this tournament. He's on 84 with the colours to come...

Stephen Hendry
Seven-time world champion on BBC Two

The thing which is going to keep Mark Williams in this match - along with his skill and everything else - is his huge temperament. He forgets disappointment and bad shots like no-one. He has the best temperament of any sportsperson I've ever known.

Mark Williams has a good chance to level this session at the interval, and bring the deficit back down to two frames.

He leads by 50 in the 12th frame.

Steve Davis
Six-time world champion on BBC Two

Great strength of character and temperament from Mark Williams. He's got the ability, like many top players, to put away what has happened and just get on with the balls in hand.

Mark Williams' break in the previous frame was the 99th of this year's tournament.

A circumspect opening to the 12th frame, with both players trying to outmanoeuvre the other with safety shots.

Judd Trump breaks through with a clever shot for a red into the left middle - however he misses the subsequent brown to hand Williams a major opportunity.

John Parrott
1991 world champion on BBC Two

In years gone by Mark Williams was never bothered by century breaks, but now with stats and the like he puts more effort in.

Image source, PA Media

The BBC's Ask Me Anything team asked for your questions about snooker during the ongoing World Championship.

Some of those questions about the sport were put to World Snooker, who have provided responses.

SKP321 asked: Why don’t the refs have an iPad with the same screen as the marker when replacing balls?

A: Nice idea! But it wouldn’t be practical for the referee to carry an iPad and the process of replacing the balls is generally fast and efficient.

Richard asked: On TV, why do they only show the table in one perspective rather than above - where we get better judgement of the ball positioning as a viewer?

A: There are several cameras following the match, including those on the arena floor showing the angles from the pockets.

Wonderfully done by Mark Williams, a break of 105 and some fancy handwork and attempted trick shots in there too.

We have a game on.

There we go, a frame safely in the bag this afternoon from Mark Williams - and he's on for a potential century break here.

He has five so far at these championships.

This is better by Mark Williams, sinking the simple shots as he builds a break through the 30 and 40s.

No-one will be counting their chickens and calling this frame won early though.