Still competing after all these yearspublished at 17:52 British Summer Time 23 April
M Williams 9-9 Si
Image source, Getty ImagesMark Williams won his first of three world titles in 2000.
Si Jiahui wasn't even born.
Image source, PA MediaSummary
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)
Still competing after all these yearspublished at 17:52 British Summer Time 23 April
Image source, Getty ImagesImage source, PA MediaPostpublished at 17:52 British Summer Time 23 April
M Williams 9-9 Si
Nothing easy for Si Jiahui right now.
Every positional shot is a pint of blood. But he's pulled out some real nerveless pots just to get this break to 27.
Postpublished at 17:49 British Summer Time 23 April
M Williams 9-9 Si
Unsurprisingly a long bout of safety to begin this decisive 19th frame.
Mark Williams is first to blink, trying a tricky red to middle but it bounces out off the far jaw and leaves Si Jiahui an easy opener.
'Unbelievable and unflappable'published at 17:46 British Summer Time 23 April
M Williams 9-9 Si
John Parrott
1991 world champion on BBC TwoIt's an unbelievable, unflappable temperament with an incredible will to win.
That's why Mark Williams has been champion here three times, he's got absolutely every credential you need and he's pulling it all out this afternoon.
'Still right at the top at 49'published at 17:44 British Summer Time 23 April
M Williams 9-9 Si
Dennis Taylor
1985 world champion on BBC TwoI remember when everyone was saying you've got to be in your 20s to win a ranking event.
He's 49 years of age this man, and he's still right at the top.
Williams takes us to a deciderpublished at 17:42 British Summer Time 23 April
M Williams 9-9 Si
The balls were positioned a tad trickier than I initially thought - mainly because reds were blocking the black going into either corner pocket.
But Mark Williams picks out a delightful plant to get everything scattered everywhere and we're going to a decider, folks!
get involved Get Involvedpublished at 17:41 British Summer Time 23 April
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Simon Woodford: If Williams wins this match he'll win the whole thing.
Postpublished at 17:38 British Summer Time 23 April
M Williams 8-9 Si
The Welshman makes 38 from that visit but misses a tough red to middle.
It's not going to matter though - Si Jiahui attempts a speculative red, aiming to screw the cue ball back to safety. But the red misses, the white hits the jaws of the middle pocket and leaves Williams the world on.
Postpublished at 17:36 British Summer Time 23 April
M Williams 8-9 Si
Stephen Hendry
Seven-time world champion on BBC TwoMark Williams' bottle and temperament is up there with the best there's ever been seen in snooker.
Postpublished at 17:36 British Summer Time 23 April
M Williams 8-9 Si
ANOTHER long red from Williams at the start of frame 18.
Admittedly this one is a tad easier than some of the others - but there was still massive pressure as he was leaving a load on for Si Jiahui if it missed.
Allen in chargepublished at 17:34 British Summer Time 23 April
Allen 6-1 R Williams
Robbie Williams has come undone here.
A break of 80 puts Mark Allen five frames ahead.
Allen goes further clearpublished at 17:32 British Summer Time 23 April
Allen 5-1 R Williams
Robbie Williams was 52 behind in the sixth frame, hit back with a break of 68 but then missed green on the colours, and that proved costly.
Mark Allen goes 5-1 ahead after a prolonged safety exchange.
Postpublished at 17:31 British Summer Time 23 April
M Williams 8-9 Si
Shaun Murphy
2005 world champion on BBC TwoI know it's not a big call with only two frames to go but it does feel like 10-9 either way.
Presenter Hazel Irvine then reminds Shaun Murphy he lost 10-9 to Si Jiahui in the first round last year...
Williams keeps his hopes alivepublished at 17:29 British Summer Time 23 April
M Williams 8-9 Si
Image source, PA MediaSi Jiahui goes in-off in the middle pocket attempting to secure a snooker and concedes.
Mark Williams is back within one frame. From 8-5 down, he's back to 9-8.
Postpublished at 17:28 British Summer Time 23 April
M Williams 7-9 Si
A delicate green is also rolled home after that last red and Mark Williams pots yellow, green and brown to leave Si Jiahui needing a snooker.
'Keeps pulling out unbelievable pots'published at 17:26 British Summer Time 23 April
M Williams 7-9 Si
Stephen Hendry
Seven-time world champion on BBC TwoWe keep saying he's not playing well this afternoon - but he keeps pulling out these unbelievable pots.
Postpublished at 17:26 British Summer Time 23 April
M Williams 7-9 Si
Si Jiahui so close to snookering Mark Williams behind the black, to the oohs and aahs of the crowd.
Those murmurs turn to whoops when Williams deposits said red flush into the top corner with a stunning long pot.
Postpublished at 17:23 British Summer Time 23 April
M Williams 7-9 Si
Mark Williams cannot get the angle to develop the red - so goes for a double.
He thinks it's in, so do the crowd, there's even applause - but it just catches a knuckle, rattles in the jaws and stays out!
50-39 to the Welshman with one red and colours remaining. Nail-biting stuff.
Postpublished at 17:21 British Summer Time 23 April
M Williams 7-9 Si
Huge counter-attack chance for Williams, this.
There's a red tight on the side cushion, the frame score is virtually level. That red is going to be key.
Postpublished at 17:20 British Summer Time 23 April
M Williams 7-9 Si
Si really taking his time over this break, knowing it could be a match-winning visit.
Focusing intently on every single shot. The reds are all there, it's just a matter of keeping calm.
But he can't! Hits a pink to the middle way too hard on 39 and Mark Williams pounces with a fantastic cut on an acute red.