Mark Allen’s chances of making the semi-finals of the World Championship in Sheffield are hanging by a thread after he finished last night’s session with Mark Williams 11-5 behind.

Williams, the 2000 and 2003 world champion, was simply too hot for the Antrim man who came back from 5-1 down to go into last night’s session 5-3 behind.

The Welshman dominated with a series of fine breaks last night, finishing with a break of 113.

He will now expect to go through to a last four clash with either Ronnie O’Sullivan or John Higgins.

Those big guns exchanged heavy fire before an overnight truce was reached in their exciting quarter-final.

From 4-2 and 35-0 behind, O'Sullivan conjured an exquisite 89 break and followed it with a rapid 105 in which referee Leo Scullion was almost chasing him around the table to respot the colours.

The official from Glasgow twice almost tripped over television cameras while the crowd marvelled at the way O'Sullivan finished the session, which ended 4-4. They resume today and have an evening finish.

Higgins never had any doubt the contest with O'Sullivan would be an experience to savour.

“It's always a great occasion, wherever you play him,” Higgins said. “He's got the Jimmy White and Alex Higgins factor. The crowd are on his side and that generates a buzz that you love playing in.

“Playing O'Sullivan anywhere probably generates the same buzz as playing in a final against most other people.”

There was mutual appreciation with O’Sullivan declaring: “He's a class player. He's been the best player in the world for the last three or four years probably. I've got great respect for John's game.”

Mark Selby was favourite for the title as he headed into his quarter-final against Ding Junhui.

But the Leicester potter faces a scrap today after Ding opened a |5-3 lead.

Selby had, a record, six centuries in his win over Stephen Hendry and began with another against Ding, 124 in the first frame.

However, Ding then strung together four in a row, featuring breaks of 58, 53, 63 and 65.

Selby made it 4-2 with runs of 51 and 87 but Ding guaranteed himself an overnight lead with 77 in frame seven. Selby finished with 74 to stay in the hunt.