It has been a morning of what could've been so far for John Higgins. We've had two frames and he will feel he should have won both of them but misses on 40 in frame 17 and on 21 in frame 18 have been ruthlessly punished.

Williams leads 10-8. He had been 5-1 down. Williams three frames away from the semi-finals.

Si Jiahui made his highest break of the match with a 101 in frame 10, for his second century of the tie.

But O'Sullivan responded in the way we expected, with a rapid-fire 75 break to restore his five-frame lead at 8-3.

In the opening frame of the day, John Higgins missed after getting 40 and he's now just missed a black off the spot after scoring 21. The Scot had been given a chance after a failed pot on a red to the middle from Williams after the Welshman had scored 49 points.

Over on table one, it looks a long, long way back for Si Jiahui as he falls 7-2 behind.

Ronnie O'Sullivan could still win it with a session to spare as needs six of the seven frames to come this morning.

'The Rocket' gave his current play a rating of two out of 10 after his second-round win.

So far this tournament, he has played 40 frames, and won 30 of them. He's going to be a real handful if he gets up to an eight or nine out of 10.

John Higgins can only sit and watch in pain knowing he should have won that frame. He got to 40 and missed a red he would've been confident of downing, and Williams did the rest with a break of 73 to nudge back in front.

John Higgins gets to 40, only to see an attempt on a red stay out, and the table is open for Williams so he could move back ahead here.

Williams was 5-1 down, then 7-6 ahead and this is a great chance to move 9-8 in front.

Higgins, sitting on a pot success rate of 90% is in first in the opening frame of the session.

Remember, 13 is the winning target, so whoever wins five frames today wins.

Michael Emons
BBC Sport

Image source, BBC Sport/Getty Images

At a combined age of 99, two of snooker's all-time greats - John Higgins takes on Mark Williams - conclude their World Championship quarter-final today.

The sport's legendary 'Class of 92', with Ronnie O'Sullivan completing the trio, have won 14 world titles between them - and are all still going strong this year.

Williams turned 50 last month, Higgins reaches his half century 13 days after this year's final with O'Sullivan celebrating his 50th birthday in December.

But they have proved that age is just a number. Could one of them again go all the way at the Crucible?

BBC Sport takes a closer look....

Meanwhile, a compelling contest between four-time champion John Higgins and three-time winner Mark Williams is delicately poised at 8-8 heading into Wednesday's concluding session.

Scotland's Higgins and Williams are part of snooker's fabled 'Class of 92', which also includes O'Sullivan.

Williams, 50, became the oldest man to reach the last eight at the famous Sheffield venue since Steve Davis did so at the age of 52 in 2010, while Higgins turns 50 on 18 May, 13 days after the Crucible final.

Yet, despite their advancing years, they remain among the game's elite set of players, with this affair reminiscent of the classic they served up in the 2018 final when the Welshman eventually triumphed 18-16.

Having watched Higgins establish a 5-1 lead off the back of four half-century breaks, Williams responded by winning six of the next seven frames, with a run of 104 the highlight in the seventh frame.

World number three Higgins dug in to win the 14th frame and appeared to have recaptured his rhythm with a 70 to edge back in front at 8-7.

However, when he missed a long red to the top right corner in the 16th frame, Williams was able to make a contribution of 65 to level the match.

Yesterday...

Ronnie O'Sullivan maintained his bid for a record eighth title in the modern era as he opened up a commanding 6-2 lead over Si Jiahui in the first session of their World Championship quarter-final.

O'Sullivan, who is appearing in only his third competitive match since January, took a scrappy opener before Si responded with a wonderful century break.

However, the 22-year-old from China uncharacteristically missed a series of pots to allow 'The Rocket' to pull clear at 4-1 with three half-centuries.

While Si responded with a 60 of his own to briefly reduce his arrears, another miss, on a black on its spot, proved costly as O'Sullivan pinched the seventh frame.

The Englishman concluded with a stylish 121 break to underline his superiority.

Quarter-finals (best of 25 frames, all matches listed to be played to a finish today)

10:00

Ronnie O'Sullivan (5) 6-2 Si Jiahui (13)

John Higgins (3) 8-8 Mark Williams (6)

14:30

Zhao Xintong 12-4 Chris Wakelin

Luca Brecel (7) 3-5 Judd Trump (2)

19:00

Ronnie O'Sullivan (5) v Si Jiahui (13)

Luca Brecel (7) v Judd Trump (2)

Welcome to day 12 at the Crucible, and what a day it is.

By the end of the day, only four men will be left in the tournament and we will know our semi-final line-up.

Ronnie O'Sullivan, Judd Trump and Zhao Xintong hold leads in their matches, while it is all square in the tie of the round as John Higgins lost a first session lead and is tied at 8-8 with fellow winner Mark Williams.

BBC Sport

The 2025 World Snooker Championship at the Crucible Theatre in Sheffield.

BBC Sport has comprehensive live coverage of the championship on BBC One, BBC Two, BBC Four and Red Button, while every match will be shown in full on iPlayer, the BBC Sport website and the BBC Sport app.

The final takes place over two days starting on Sunday 4 May.

To read the full guide for draws, results and coverage, click here.

Image source, Getty Images

Get Inspired
#GetInspired

Why get into snooker, billiards and pool?

They are non-contact, indoor sports which can be played competitively or socially.

Who is it for?

Snooker, billiards & pool are skilful games that can be played by anyone, regardless of age, gender or ability.

Is there a cheap option?

Many clubs allow you to borrow equipment and membership fees can be inexpensive.

Is it good for my health and wellbeing?

Cue sports provide a fun and sociable way to stay active, improve your concentration and increase your strength and muscle control.

Can I take it to another level?

Once you've mastered the skills, you could enter local league matches and amateur level competitions across the country.

Is there a disability option?

Cue sports are very inclusive as the rules and equipment are the same for able-bodied and disabled players.

Is there a family option?

Many clubs welcome junior members. You can also play in teams and use a handicap scoring system.

Snooker, billiards and pool all offer different challenges, but from pubs to clubs to competition, they offer an accessible option for anyone hoping to pick up a cue.

It shouldn't be hard to find somewhere to hone your skills. What's more, an official snooker club finder, external was launched in 2018 to help you find the perfect place to play.