Result: Robert Milkins 10-9 Pang Junxu
End of session: Barry Hawkins 4-5 Ryan Day (first nine frames)
Result: Three-time champion Mark Williams beaten 10-9 by Si Jiahui
End of session: Mark Allen 7-2 Robbie Williams (resumes 14:30 BST Wed)
End of session: Ding Junhui 4-5 Jack Lisowski (resumes 10:00 Wed)
End of session: Kyren Wilson 8-1 Dominic Dale (resumes 10:00 Wed)
M Williams 7-9 Si
Dennis Taylor
1985 world champion on BBC Two
You've got to be so impressed by this 21-year-old.
He was wonderful last year, looked like he was going to be the youngest winner ever, taking Stephen Hendry's record which has lasted for so many years.
He was awesome last year and he's been brilliant in this match against Mark Williams.
Image source, Getty ImagesM Williams 7-9 Si
Wonderful, wonderful middle-distance red from Si Jiahui after a Williams miss.
Even better as he was slightly put off by noise from the adjoining table and had to get up off the shot before re-composing himself to bang it in.
M Williams 7-9 Si
Mark Williams gets in a couple of times early on in frame 17 - he's in last-chance saloon, remember.
But things don't go to plan and he's tempted into a long red that stays out. He could have left Si something easier than a tough red to middle which also misses.
M Williams 7-9 Si
Dennis Taylor
1985 world champion on BBC Two
He's held himself together well, Si.
This is a terrific performance after what had happened in the last couple of frames. Every credit to him.
M Williams 7-9 Si
After all that, though, Mark Williams leaves a red over the corner.
Still plenty of work for Si Jiahui to do but he pulls out a number of cracking pots to take the frame with a break of 48 - and move one frame away from a stunning upset.
M Williams 7-8 Si
And here's Williams' one-handed shot in return.
Off two cushions and flicked off the pack of reds back to baulk.
Image source, BBC SportM Williams 7-8 Si
Here's where Si Jiahui managed to get Mark Williams in behind the green from.
White ball right in the jaws, he flicked off the red near the blue, back up off a couple of cushions and behind the green.
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Owlsfan83: This is brilliant to watch. Willo proper doing everything he can
M Williams 7-8 Si
Some of the shots here.
Two-cushion escape out of a snooker from Si Jiahui, who, a couple of shots later, has to play the cue ball from the jaws of the green pocket but still snookers Mark Williams in return.
Williams responds with a trademark one-handed escape. Yes, one-handed! He plays that shot sometimes as he feels it gives him better control when near a cushion.
Allen 4-1 R Williams
That will be annoying for Robbie Williams.
He was on a potential frame-winning break of 44 before coming unstuck and could not recover. Williams won't want to lose too many of this afternoon's remaining four frames.
M Williams 7-8 Si
Dennis Taylor
1985 world champion on BBC Two
Is the pressure starting to tell now on this 21-year-old?
Because that was a nervy one, that miss.
M Williams 7-8 Si
Those two post-interval frames took almost an hour between them.
Has that derailed Si Jiahui's momentum?
Well, he's in first in frame 16 after an attempted fine cut by Mark Williams leaves a red over the pocket but the Chinese can only make 33 before missing.
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Image source, PA MediaShould the tournament stay or move from the Crucible Who will win? What's the state of the game right now?
We want your snooker questions - fire them in, and we will get one of the BBC snooker team to answer later in the week.
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Michael Emons
BBC Sport at the Crucible Theatre
Image source, Michael EmonsMeet Johnny Potalot, snooker's first mascot. It's a chance to grab a memorable photo outside the Crucible and see smiles being put on fans' faces.
Paul Jamieson is the man in the suit and was getting a great reaction from people of all ages.
He said: "I launched it in 2023 and it's been an idea of mine for 25 years, thinking snooker does not have a mascot and I think it's what is needed to interact with the fans on the approach to the venue.
"The reaction from the fans has been great and it has exceeded my expectations. When I first launched it in York, I was meeting and greeting fans as they arrived and people were tooting their horns and hanging out of cars taking photos. The adults are bigger kids than the children and they love it.
"Last year there were some ladies who were going to watch Blood Brothers at the Lyceum Theatre next door to the Crucible and they were all running over taking photos and that's all good for promoting the sport.
"The World Snooker Tour are trying to make it more family orientated and get kids involved and even the likes of this mascot does the trick."
Image source, Michael EmonsM Williams 7-8 Si
Si leaves a red on after escaping the snooker and, after a funny moment where Mark Williams asks the ref to clean the red in the hope of inching it closer to the pocket upon its replacement, the Welshman pots the remaining balls required.
A quite fantastic long blue to the corner with the cue ball on the baulk cushion is followed by an equally brilliant red.
He tries to hammer in a black ball too and it flies off the table! Anyway, it's back to 8-7.
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Si Jiahui almost looks shocked at some of the pots Mark is making. Mark using all of his experience and guile to slowly get back into this match. Brilliant watch.
Luke
M Williams 6-8 Si
Wonderful safety shot upon his return from the bathroom by Si Jiahui.
Was he perusing Steve Davis' Book of Safety Shots during his toilet break?
If so, it seems Williams had a read too - as he replies with an even better effort that has Si snookered.
M Williams 6-8 Si
Bit of a marathon frame this one. So much so that Si Jiahui needs to take a trip to the loo while it's still going on.
Mark Williams decides he's going to nip out too.
M Williams 6-8 Si
Is that the difference in this frame?
Mark Williams finds himself in a pickle but pulls out a cracking safety, cushion first to clip a red and leave everything safe.
Si Jiahui in just as much trouble - and he can't find an answer, leaving Williams an easy starter. He pots a couple but breaks down again.
M Williams 6-8 Si
Goodness me, Mark Williams fires a black into the corner that must have rattled about 20 times in the jaws before it dropped.
Big opportunity now for the three-time world champion to pull back within a frame.
But he misses a routine black soon after - perhaps put off by a spontaneous burst of applause on the neighboring table.
Image source, Getty Images