Williams does well to find a way through to edge the red into left middle, but the following blue stays out and Trump has a chance to make a big score in the second frame.

Ken Doherty
1997 world champion on BBC Two

Judd Trump had Mark Williams in some trouble there and he'll be relieved to win it. Starting a best-of-33 semi-final with a frame like that - fantastic.

Judd Trump may be regretting now not going to push for the respotted black as his attempt to get a third snooker ends when Williams pots a fortunate red. His break of 72 is the difference and the Welshman wins the first frame of eight tonight.

Image source, PA Media

Shaun Murphy
2005 world champion on BBC Two

It feels like this first frame has taken on even more significance in the past 10 minutes.

Now Williams fouls again so if Trump clears the table from here the scores would be level and it would go down to a respotted black, so Trump persists with the safety game looking for a third snooker.

Williams gets out of one snooker, only to find himself immediately in another, tougher one and this time the escape attempt goes wrong to give Trump one of the two fouls he needs.

Trump makes 30 and sticks the cue ball tight behind the pink, with the red sent down table.

Trump does at least get another shot, but is 4-77 behind, with two snookers needed.

Mark Williams has taken full advantage of that Judd Trump error. He's up to 73 and still going, Trump needs snookers.

BBC Two

You can watch this semi-final live on BBC Two until 20:00 BST, when coverage switches to BBC Four for the remainder of the evening.

It's also available on the BBC iPlayer and at the top of this page by clicking on the "Watch and listen" tab.

Steve Sutcliffe
BBC Sport at the Crucible Theatre, Sheffield

Image source, Getty Images

There has been a lot of talk about Ronnie O'Sullivan's cue at different stages of the tournament.

He's had cues from at least two different manufacturers at his disposal and he brought two to the Crucible last night for his 13-9 quarter-final win over Si Jiahui.

So you get the impression there has been a bit of chopping and changing to get something he is entirely happy with since snapping his old cue at the Championship League in January.

So much so that he has dropped off the cue he used this afternoon against Zhao Xintong at a local snooker cue shop in Sheffield this evening to change his titanium ferrule to brass and get a new tip.

After a foul apiece, Judd Trump goes for a long red, but there is another one in the way. Trump thinks he can swerve around that one and pot the other one, but he hits the wrong ball and Williams has a great chance now to get some points on the board.

Shaun Murphy
2005 world champion on BBC Two

To get yourself into that pantheon of greats, you have to be a multiple world champion. There's a special place in history reserved for players who have managed to take this trophy home more than once.

World number one Judd Trump is a prolific ranking event winner but has won the world title just once, back in 2019.

Great receptions from the fans and away we go. Mark Williams misses a long red first up, so here comes a high-quality safety battle.

Mark Williams came through a Crucible thriller against fellow veteran John Higgins to reach the last four.

Watch the closing stages of that fantastic contest below...

Steve Davis
Six-time world champion on BBC Two

When you get to this stage, you know you've arrived, even though you're still so far away from winning the title.

All eyes are on you, the intensity in the room magnifies and everybody who comes in the room is just watching the one table.

If you can play well on this stage, you're some type of player.

Ken Doherty
1997 world champion on BBC Two

The way Mark potted those last few balls against John Higgins was incredible. He's just so cool under pressure.

He's been one of the icons of the snooker world and he's still playing wonderful snooker, even at the age of 50.

Steve Sutcliffe
BBC Sport at the Crucible Theatre, Sheffield

It is boiling hot in Sheffield at the moment and if you are grabbing an ice cream in Peace Gardens it's quite likely you could see a famous face from the world of snooker.

Danielle counts John Higgins, Shaun Murphy, Mark Williams and Jimmy White among her customers but says she is still patiently waiting for Judd Trump to pop over.

"I've seen him walk past a few times, so hopefully he comes across to say hello," she said.

Earlier today, Ronnie O'Sullivan and Zhao Xintong shared the first eight frames of a highly-entertaining opening session of their World Championship semi-final.

Zhao potted a black in the final frame which left the table fitters with some work to do before play resumes this evening...

Image source, PA Media

The Crucible has had a bit of a transformation since the quarter-finals were completed on Wednesday evening.

The main arena now hosts just one table rather than two, with only one match taking place per session until the world champion is crowned on Monday.