Barry Hawkins has the edge over Ronnie O'Sullivan after classy opening session
Ronnie O'Sullivan's quest for a sixth World Snooker Championship is under threat after in-form Barry Hawkins edged the first session of their quarter-final.
Hawkins, beaten by O'Sullivan in the 2013 final, will take a 5-3 advantage into Sunday afternoon's resumption after a high-quality opening which included three centuries.
O'Sullivan, who had received a formal warning on Monday for failing to fulfil media duties in the wake of his first round win against David Gilbert, dropped the first frame but bounced back with a superb 139 total clearance.
The enigmatic 40-year-old went on to raise early hopes of a maximum in frame three, but after firing 25 and splitting the reds beautifully, he missed a black off the spot.
And if O'Sullivan ever doubted he had a battle on his hands, the size of his task was underlined as Hawkins calmly responded by clearing up with a 102 to take a 2-1 lead.
Back-to-back breaks of 88 and 102 nudged O'Sullivan back in front, but Hawkins got the better of each of the last three, more attritional frames of the session to establish his two-frame overnight lead.
Elsewhere World Snooker confirmed it will bring forward a scheduled replacement of cloth and cushions at the Crucible following complaints by players.
Ali Carter criticised what he called the worst conditions of his career after letting slip a 9-7 overnight lead to lose his second round match 13-11 to Alan McManus.in the morning session.
Carter, a two-time Crucible runner-up, said: "The conditions were absolutely horrific - there were kicks every other shot and big bounces.
"I don't think I've played on a table that bad in my career. It's the same for both players but it's how it affects you mentally."
The 36-year-old lost the first four frames of the morning session to hand the initiative to McManus, who duly booked his last eight place for the second time in three years at the age of 45.
McManus said: "I could sense (Carter's frustration) and I could understand why, with the conditions being quite trying out there on our table.
"It can spoil your game totally so I thought 'right, just tough it out here - I'm going to get some dodgy bounces but try to get some chances and keep the white from not using too many cushions' - that's kind of crazy but I was thinking that."
The conditions - which appear to be specific to table one - were also criticised by former winner Mark Williams after he booked his place in the last eight with a 13-8 win over Michael Holt.
Williams had taken matters into his own hands in the opening session on Friday when he risked censure by wiping down the cushions, and he picked his words carefully.
After booking his place in the last eight for the first time in five years, Williams said: "I think I know what the problem is but I can't say it up here because I'll get fined.
"The bounces we've had for so long now are so frustrating because they've got the solution in the office right now - it's only a tiny thing they've got to do and it will get rid of bounces instantly, but they just won't use it."
Williams will face either Judd Trump or Ding Junhui in the last eight, and believes he has a chance to go further if he maintains the form which saw him recover from a poor first session to cruise to an impressive win.
"I'm just happy to be here," added Williams. "I'm normally watching the quarter-finals in the house so it's good to be involved. I'm just going to enjoy it and if I keep playing like I am I'll be tough to beat."