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 5-5 Si
Image source, BBC SportThis was where Si ended up after that final red that was over the pocket.
But he banged in a nerveless brown to finish perfectly on the yellow and went on to take the frame to level the match.
M Williams 5-5 Si
Shaun Murphy
2005 world champion on BBC Two
That brown showed you Si is full of confidence.
But he shouldn't have been there [in that position with the cue ball].
It's those little things - it didn't get him that time but it might get you later on in the event. It's those little mistakes you have to tidy up.
M Williams 5-5 Si
A below-par positional shot on that red gives Si Jiahui work to do - but he knocks in a brilliant brown with the cue ball near the cushion before mopping up the colours.
The Chinese prospect is back level.
M Williams 5-4 Si
Si Jiahui has had a couple of chances to level this match by taking this opening frame of the afternoon.
But he hasn't been able to do so - and Mark Williams has knocked in a couple or three cracking reds to haul himself back into it.
Cuts the deficit to 18 points - big shot on the final red along the side cushion... it stays out and leaves Si a gimme.
Allen 2-0 R Williams
A missed yellow proves costly for Robbie Williams - it allows Mark Allen in and he's now two ahead.
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Ref. Michael's 14:16 post - a great summary of the Robbie Williams v Mark Allen match. Let's hope that Robbie has the Freedom to play his normal game and doesn't do Somethin' Stupid. If he plays with confidence and wins this match, he has the potential to achieve Something Beautiful!
Mick Green, Bolton
Michael Emons
BBC Sport at the Crucible Theatre
Image source, Michael EmonsSome fans are regular visitors to the Crucible every year, but for some it might be a once-in-a-lifetime trip to the home of snooker.
If so, you might want to leave with a souvenir. And you're not short of options.
T-shirts, coats, jumpers, fridge magnets, pictures, teddy bears, programmes, art work, books, mugs, pens - the choice is yours.
Image source, Michael EmonsM Williams 5-4 Si
Si Jiahui sending out a real warning sign to Mark Williams.
If you miss, I'm going to make a few. He has to be content with 43 on this occasion as an attempt to break into the pack off the black leaves him on nothing.
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Mark Allen could be in for a tough game this afternoon because I've heard that Robbie Williams loves angles!
Jon in Leek, via WhatsApp
That's worse than some of my puns earlier, Jon...
M Williams 5-4 Si
"Highly unlikely you would make a plant with the distance between those balls."
So says Dennis Taylor on commentary as Mark Williams, cue ball near the baulk cushion, lines up a very speculative plant with two reds miles apart.
And, of course, in it goes.
Misses a red soon after though and Si Jiahui has a decent chance to establish a healthy lead in the first frame of this decisive session.
Allen 0-0 R Williams
Let Me Entertain You?
Take that - Robbie Williams (the snooker player) chose not to walk on to Robbie Williams (the singer).
The Meryseyside potter came out to Feelin by Liverpool band The La's...
Northern Ireland's Mark Allen arrived to the strains of Can't Stop by the Red Hot Chilli Peppers.
Image source, Getty ImagesShaun Murphy
2005 world champion on BBC Two
I'm sure he doesn't tailor his season around this tournament, but it's a bit like your driving test - you get your licence and then you learn to drive.
Life on tour is like that. He should have won the semi-final last year and now he's got to learn to drive.
To some degree he's gone missing in the past 12 months, but he's back.
M Williams 5-4 Si
John Parrott
1991 world champion on BBC Two
For somebody aged 21, Si knows a heck of a lot.
He's had a wily old fox against him yesterday in Mark Williams, who can pot balls but really tie you up as well - and Si matched him in all departments.
It was just the last two frames - Mark was 4-3 behind and he could see the danger signs, and he played two very good final frames just to put his nose in front.
M Williams 5-4 Si
Image source, BBC SportFew players have more memorable World Championship debuts than Si Jiahui experienced at the Crucible last spring. He beat Shaun Murphy 10-9 in a first-round thriller en route to reaching the semi-finals - the first debutant to do so since 1995.
But the Chinese went from ecstasy to agony, letting slip a mammoth 14-5 lead over Luca Brecel in the semis as the Belgian won 12 of the final 13 frames to triumph 17-15 on his way to lifting the title.
The 21-year-old took a while to get over that, with several early tournament exits at the start of the season, but he reached his first ranking final at the German Masters in February, losing to Judd Trump.
And, after keeping pace with Mark Williams in Monday's first session, the world number 23 will harbour hopes of shocking a former Crucible champion in round one for the second year running.
Former World Championship runner-up Kyren Wilson was in impressive form this morning as he stormed into an 8-1 first-round lead against Welsh veteran Dominic Dale.
Twelfth seed Wilson produced a superb performance with breaks of 52, 75, 123, 96, 50, 77 and 73 to only need two more frames when the match resumes on Wednesday morning.
Dale, 52, is the oldest player at this year's competition and playing at the Crucible for the first time in 10 years.
England's Jack Lisowski, 17th in the world and who only narrowly missed out on automatically qualifying for the tournament, holds a 5-4 advantage following a high-quality session against 2016 finalist Ding Junhui.
Read Michael Emons' full morning report from the Crucible here.
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Image source, David TrenholmWe trust David enjoyed the morning session!
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Allen v R Williams
Michael Emons
BBC Sport at the Crucible Theatre
Image source, Getty ImagesRobbie Williams lost in the first round in 2016 to Ricky Walden, in 2015 to Stuart Bingham and in 2014 to Neil Robertson
Robbie Williams is back at the Crucible for the first time in eight years, after losing in the first round in 2014, 2015 and 2016.
Ranked 45th in the world, the 37-year-old has already had to fight through two rounds of qualifying across Sheffield at the English Institute of Sport.
He knocked out Anthony Hamilton and then beat Chris Wakelin, a player 25 places higher than him in the rankings, in a nerve-shredding final frame decider to secure his Crucible return.
"It was pure relief," said Williams. "Nothing is granted in this game and it's eight years since I’ve been there and you start to worry a little bit, but I always fancied myself.
“The last three times I’ve been there I didn’t do myself justice so time to show what I’m made of on the big stage.”
Allen v R Williams (14:30 BST)
Michael Emons
BBC Sport at the Crucible Theatre
Image source, Michael EmonsTwo players from Northern Ireland have lifted the world trophy at the Crucible - Alex Higgins in 1982 (for his second world title) and Dennis Taylor three years later in the legendary 1985 black-ball final win over Steve Davis, regarded by many as the greatest match the venue has ever seen.
It has been 39 years since Northern Ireland has had a world champion, but that could end soon as Mark Allen, a semi-finalist in both 2009 and 2023, comes into this tournament as the world number three.
The top half of the draw in which Allen finds himself has already seen top seed Luca Brecel, fifth seed Mark Selby and ninth seed Ali Carter all lose inside the opening three days.
"I have won three tournaments and I'm up there in the one-year list and world rankings, but I don't feel I'm playing as well as I would like," said Allen. "I have a chance of winning even if I don't play well, which is a great place to be."
Allen will be seeing this as a great chance this year and starts off with a tie against Robbie Williams, who at 45th in the world, is the lowest ranked player at the tournament.
Allen v R Williams (14:30 BST)
Image source, Getty ImagesThere's another Williams in action on the other table this afternoon - Robbie Williams (no, not that one) is making his first Crucible appearance since 2016.
That must Feel like an Eternity.
The world number 45, the lowest ranked player to qualify for this year's tournament, has Come Undone in the first round on all three of his previous visits.
He faces a tall task to improve that record, having been drawn to face world number three Mark Allen. Will Robbie be the Better Man and have No Regrets?
Or will Allen be too Strong and reign Supreme?
M Williams 5-4 Si
Image source, BBC SportIt's hard to believe Mark Williams is 49 years old.
Only a fortnight or so ago, he claimed the 26th ranking title of his career, producing a superb performance to beat Ronnie O'Sullivan 10-5 in the Tour Championship final.
Williams, who has also lifted the British Open title this season, beat Judd Trump and Mark Allen en route to the final before reeling off seven successive frames from 5-3 behind to down 'The Rocket'.
Could he win a fourth Crucible crown? Few would back against it.