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End of Session: Chris Wakelin 4-12 Zhao Xintong - Table One (9th to 16th frame)
End of Session: John Higgins 8-8 Mark Williams - Table Two (9th to 16th frame)
Afternoon end of session (Resumes Wednesday 10:00):
Ronnie O'Sullivan 6-2 Si Jiahui
Judd Trump 5-3 Luca Brecel
Quarter-final matches played to the best of 25 frames
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That's just about your lot for this evening's coverage of the World Champonship.
We will, of course, be back on Wednesday with live coverage of all the key pots from the quarter-finals in Sheffield on the BBC Sport website.
In the meantime here's some other snooker stories worth a read:
Quarter-finals
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)
Ken Doherty
1997 world champion on BBC Four
Without doubt Mark Williams will be the happier of the two players. He's won the session tonight.
Higgins 8-8 Williams
Higgins 8-8 Williams
John Virgo
1979 UK Championship winner on BBC Four
It was supposed to be a moving day but not much has moved. What a match we have in store tomorrow morning!
Higgins 8-8 Williams
A break of 65 from Mark Williams is followed by a foul from John Higgins who insists on playing on despite needing snookers. Eventually, Williams dispatches the pink to seal the frame.
We end the session all square.
Higgins 8-7 Williams
Image source, Getty ImagesIt's looking like we are going to end the evening all square. Mark Williams have a break of 57 and is on the cusp of leaving John Higgins snookers.
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Higgins v Williams takes me back to the "nip and tuck" snooker I watched in the early 1980s. Not as many one visit frame wins in this match.
Paul in Dublin
Higgins 8-7 Williams
John Virgo
1979 UK Championship winner on BBC Four
John Higgins appears to have rattled Mark Williams and he's hardly potted a ball since. It shows you psychologically how things can turn.
Higgins 8-7 Williams
John Higgins makes the early running in the final frame, but Mark Williams have just broken the pack up and looks well placed to work round the pink.
Wakelin 4-12 Zhao
Zhao Xintong was far from convincing at times, but he's 12-4 up on Chris Wakelin and needs just one frame on Wednesday afternoon to seal a semi-final place.
The most likely opponent in the last four is Ronnie O'Sullivan. Master v Apprentice?
John Virgo
1979 UK Championship winner on BBC Four
Final frame of the session coming up, and it's a big one.
Higgins 8-7 Williams
John Higgins eventually finds some rhythm at the table and a break of 70 gives him back-to-back frames. He's battled through a tough patch and has now got his nose in front again.
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Dafydd Jones: People love to moan about Selby being slow or grinding down opponents, but Higgins is equally as bad when things don't go his way. Horrible player to watch at times.
Higgins 7-7 Williams
John Higgins nurdles his way to 32 points but offers Mark Williams a chance on a long red. The Welshman takes it on only to see the ball hit the jaw of the corner pocket. It feels a key moment for Higgins as he returns to the table.
Wakelin 4-11 Zhao
Steve Sutcliffe
BBC Sport at the Crucible Theatre, Sheffield
After winning the opening two frames this evening, Chris Wakelin has simply not been able to keep any sort of foothold in this match.
He has not had a great run of the balls but he has been out potted and looked ill at ease with his opponent ruthlessly closing towards a semi-final spot.
This match resumes at 14:30 BST on Wednesday. The way things are looking, it could be done and dusted before school pick-up.
Wakelin 4-11 Zhao
Plenty to ponder for Chris Wakelin as he trails Zhao Xintong 11-4.
He needs to win nine from 10 frames.
Higgins 7-7 Williams
John Virgo
1979 UK Championship winner on BBC Four
Whatever happens in the rest of this session it will be all to play for tomorrow you sense.
Higgins 7-7 Williams
Gritty snooker from John Higgins as he rolls up his sleeves - not literally - and grafts out a tactical frame in his favour, It was not one for the purists, lasting just under 40 minutes, but it has got him back on level terms with Mark Williams.
Higgins 6-7 Williams
John Higgins is fighting hard in this safety battle for the 13th frame. The Scot has a 23-point lead over Mark Williams with 35 remaining on the table.
This has been an arm wrestle of a frame.